Molding Flash & Flashing is one of the most important potential problems.

Flash & Flashing occur

Flash can occur during injection filling  or during the pack/hold stage, and it can occur any kind of conventional parts ,especially easy happen of thin-walled parts with high MFI material . Discovering in when flash occurs helps to be responsible for the problem simplification . A simple test is to bring the pressure to the minimum the machine allows, Limitations lie is the plastic pressure  should be below 500 psi . The aim is to see the effect of just barely filling the cavity. First step is injection fills 92% to 99.9% of the part, but the cavity is full then stop there. At the minimal pressure level we can easy to inspect  If there is flash happen on the short shot,then we should do is  focus on parameters adjust during injection. If no flash happen after a short shot, then we should go to another way to adjust the transfer point to avoid over-filling the cavity.

molding flash


When designing your plastic parts, as far as possible to reduce the thin-walled section, resulting in a thicker wall section, the entire product into a uniform wall thickness of the parts.

The rapid change in wall thickness is the most common cause of flash, due to the production process of plastic materials under pressure, through the liquid state to fill the injection mold.

If the product design in the thick and thin wall thickness of the part is necessary to exist, the use of different injection point to help the flow of materials.It is very important to control the location of the gate, especially in the tight tolerances of the plastic parts.

Flash of an injection molded part can happen for several reasons – slight variations in the material, pressure, speed, injection mold process and/or problems with the tooling itself.

For example,The sprue bushing is one of the reasons that can not be ignored.Need to know is that nozzle contact forces can range from 5 to 15 tons.If the thermal expansion makes the critical distance sleeve “growth” out of the parting line, the nozzle contact force enough to move the mold side, resulting in flash generation not only mold precision will produce flash operation,The operation of the injection molding is the same as the source of the problem, the mold should take advantage of the length of the hot runner bushing inspection, into the standard of each production.

Through analyze every stag of the injection molding process at our company, and ensuring consistent stress free manufacturing of your custom plastic parts.Our process engines allow us to produce tight tolerances parts for all of our customer.



in plastic injection molding industrial, it refers to part features that prevent straight ejection at the parting line, which cause much mold complexity and lead to higher mold construction and maintenance costs. Whenever it’s possible, redesign the part to avoid undercuts. Minor part design changes can often eliminate undercuts in the mold. For example, adding through holes can give access to the underside of features that would otherwise be undercuts, simple modifications enable the mold to form a hole in the sidewall rather than with a side-action mechanism.

  • Side-action moulds are available with our standard manufacturing time of 5 working  days only. we always give customer most quickly service than any other company in china, actually more quickly than US, or Europe injection molds maker.
  • Side Action Support for Simple Undercuts or complicate undercut with difference manufacturing way.

At Cnmoulding  any number of undercuts we have the capability to produce your custom parts design. Our precision mold making technologies allows us to provide you the highest quality service , it will delivers the most complex plastic injection molded parts in the industry.


  • Injection Molding Undercuts ,the features is we don’t make it on the parting line area, it will cost much high fee and not easy to finish ejector part out.
  • Undercuts typically lead to increased whole injection molds complexity , it can lead to higher invest a mold construction costs as well.
  • The use of the most simple product design, do not add too much ribs, you can save the cost of the mold, so as to better design of plastic parts and more efficient molding process

Either an internal undercut or external undercut construct, when mold design it  requires an extra a slider or lifter structure to capture the detail of it. When an undercut feature cannot be removed from the part design, the tooling will most likely require for example hydraulic cylinder mechanisms  or gas assistant mechanisms to help facilitate the ejection out.

Know about knit lines

About Knit Lines

The plastic injection molding process is simple standard job , plastic raw material  is heated to its melting point ( for example ABS resin), it was forced into your injection molds to produce your plastic parts through injection molding machine. The molten material is often the coolest surface and to solidifying at all of leading edge .

Knit Lines

When the molten plastic meets an obstruction, then the flow resin must travel around and meet at the other side.  It can easy happen knit lines on plastic parts surface when they meet past an obstruction, If the plastic has too much cooling  during the plastic injection molding process.

Cnmoulding technicians try to minimize any knit lines, but we must balance this with other challenges like avoiding sink mark or blush, to achieve the perfect surface. So what we can do to help avoid knit lines happen when designing the new part at beginning.

Here are a few things should be consider.

  •  Big thickness part design will slow down the cooling rate of the plastic resin ,so help to improve the appearance of knit line.
  •  Difference plastic resin selection is one of variable quantity. Fiber glass resin have less knit lines than normal materials,Fiber rought surface will cover knit lines. In fact, additives like flame retardants, lubricants and mold releases can further exacerbate the problem.
  •  Cnmoulding will optimally place the gate so that the knit lines are minimized ,usually it should move to a less critical area through improve our job.

If you are concerned about potential knit lines happen in your new project ,use CAE software to analyze mold flow of your part and address any design issues that can be easily modified, and review similar plastic resin that may be good way to show knit line position there. Remeber ,good industrial design and injection mold design, improve right gate point , knit line can often be reduced easy.

Five technological ingenuity to solve injection molding plastic deformation method

Five technological ingenuity to lead you solve when injection molding plastic deformation method

plastic injection molding parts

The causes of deformation
1) the shape of products, especially forming shrinkage relationship with product thickness caused by residual stress
2) Due to the forming conditions of residual stress in
3) parting the residual stress produced in
4) and deformation due to insufficient cooling time

2. The associated knowledge
1) the deformation of the products (warping, bending, small wrinkles) as well as the reasons of the crack.The residual internal stress in the products.Molding set conditions should be set in eliminate products of internal stress direction. Namely improve material barrel temperature and mould temperature, the material liquid get better state, the injection pressure is not too high.
2) in order to reduce the residual stress, annealing processing, namely under thermal deformation temperature of 10 degrees, more than 2 hours of heating has the effect of stress relief. But this way because of the high cost of annealing and use is not common.
3) if the mould cooling hole not to cooling homogeneity of products, also can produce residual stress, which means that the cooling hole can’t be too shallow.

Third, solution.
1) instant: sufficient cooling solidification in the mould (chronograph longer cooling time), and improve the temperature of the material, reduce the injection molding pressure.
2) short-term: make mold cooling uniformity.
3) long-term: avoid the thickness of products, where product thickness large set gate (1-1), caused by a straight line easy to warp, make it big R curve, products reversible bending die, increase the number of ejection rod, increase the draft.

Four, differences in material:
1) the crystalline materials (poly (PVC), polypropylene, pom, nylon),injection molding shrinkage rate, and easy to cause bias, non-crystalline material (polystyrene (PVC, ABS) easy to cause residual stress.

Five, the reference items:
1) use orthotics keep at room temperature after molding, to prevent deformation, slightly but not hope too much.
2) in the box forming of thin shape, bending caused by injection molding temperature, this is common thermal expansion

Plastic Injection Molded parts Quality Control 100% Inspection

100% plastic Injection molded parts quality inspection methods
In China,Whether produced after injection products meet quality standards, must be tested, a common quality test methods are the following few ways.

injection molded plastic in china

injection molded parts inspection in china

  •  full inspection

It was called full inspection is individually tested for injection products, we have talked about “full” refers to the number of all the plastic parts produced, rather than the entire value of the quality characteristics tested. In determining the test items,Test costs are generally low, the implementation of all product inspection is to have a higher quality requirements.

Such as plastic parts Dimensions test is easier and can be fully tested, and the requirements of the position and some plastic parts crucial, a great impact on the quality, but also the need for full inspection. Not plastic parts for each test must be carried out in full, as it cost too much time-consuming and laborious. Usually occurs when the following conditions using full inspection.

1) found that more unqualified plastic parts, plastic parts or the whole batch are unqualified, the need for follow-up products for full inspection.

High single value

2) injection products, even when a scrap will bring great losses.

3) If the product quality problems, give people life safety or safety hazard when great.

  •  Injection molded plastic sampling inspection

The so-called sampling inspection,, is from a group of randomly selected plastic part of the test conducted. By this test section of plastic parts extracted to make the evaluation of quality of these plastic parts. Compared with the full inspection sampling inspection, it tested a small number of plastic parts, low-cost test, test speed. Sampling inspection and batch size of the number of samples, volume, sample quantity; small quantities, less sampling; as long as the appropriate number of samples, the test results have a high accuracy. Usually by random checks in the following cases.

1) Some of the Injection molded plastic parts that  mechanical and physical properties need to destructive testing, this will bring damage to the plastic parts.

2) more than the mass production of plastic parts, plastic parts produced quantity particularly large, want to save test time and test costs.

3) the production of raw materials in Injection molded plastic parts, there are a lot of raw material is powdered, granular or liquid form, the raw material for these multi-use sampling. Compared with the full inspection sampling inspection, although there are a small number of test and low test cost advantages, but also the following problems: First, when the second installment of the plastic parts, even after sample testing has been considered qualified, can not believe that this batch of plastic parts plant each plastic parts are qualified, which may also exist a very small amount of non-conforming product. Second, the sample tests will inevitably appear judgmental errors, this is the vast majority of qualified products, due to sampling bias, but judged unqualified; or could have been substandard goods, has become qualified. Therefore, in order to determine the probability of error is controlled within a reasonable range, often need to coordinate the use of mathematical statistics methods.

In short, the full inspection and sampling test has its own characteristics, and applications and problems also vary, depending on the circumstances test methods should be chosen to adapt. Mostly due to the injection mold products for mass production, it is more to take sample tests

  • Machine Inspectioninjection molding molded plastics inspect

Parts are initially inspected directly out of our molding machine. Our engineers are trained to identify and rectify the following defects:

  1. Sink marks that form when the outer plastic shell hardens before the internal plastic has had an opportunity to cool
  2. Short shots caused when there is an inadequate amount of plastic material to fill the mold
  3. Burn marks caused by trapped compressed air during the molding process
  4. Flash marks, which is the excess plastic that extends from the end of the molded part

Precision injection molding production, process and machine selection

Process flow difference between Precision injection molding and the common plastic molding 

The characteristics of precision injection molding is: the size of the injection molded parts with high precision, small tolerance.

precision injection molding

precision injection molding

To achieve the requirements of precision injection conditions must be met:

(1) the mold material is better, rigid, cavity dimension precision and template between positioning accuracy is higher, lower surface roughness.

(2) to adopt precision plastic molding machine.

(3) to adopt precision molding process.

(4) to choose suitable for precision injection molding process of the material. Commonly used precision molding materials have several: POM, POM = CF (carbon fiber), PNM = GF (glass fiber), PA \ FRPA66 (enhanced PA), PC, etc.

Precision injection process can ensure the size ,that molding is the important way to control the shrinkage of injection molded parts, including: thermal contraction, disguised contraction of molded parts, orientation and compressed contraction and elastic recovery.

Common injection molding features not high than  precision injection molding, the size of injection molded parts are typically can be assembled into standard, requirements for the appearance of the injection molded parts is relatively high, if necessary, may use the second processing (oil, for example) to improve the appearance of defects. Ordinary injection molding don’t need to use special precision injection molding machine, also do not need to specially designated materials, general common thermoplastics can be used to production. So ordinary injection molding technology is widely used in modern plastic industry.

Precision injection molding process

In the process of precision injection molding, the raw material is pre- loaded into the box.
Automatic feeding (in the form of particles) to the injection molding machine hopper.
Melt the raw material in the barrel and inject the mold under high pressure.
The molten polymer is allowed to cool and solidify, and is removed from the mold.
If necessary, used water to clean, dry with a hair dryer. Then they are shipped for packing inspection.

Medical supplies and equipment for precision semiconductors as well as data storage, consumer electronics, medical and automotive industries in the production of precision injection molding of other high precision plastic parts.

Various tonnage of automatic precision injection molding machine (from 80 to 650 tons), our products meet the customer’s strict size, functional and aesthetic requirements.
We also provide medical products, the formation of non dust production plant, clean the packaging of various products, molding parts without pollution risk.

Select a good precision injection molding machine

To buy a high precision injection molding machine, the impact of injection molding machine selection factors include the following:
1 die size (length * width * height), weight, special design
2 kinds of plastics (pure or many kinds of plastics)
3 injection product size (L, W, H, thickness), weight and so on.
4 molding requirements: such as quality conditions, production speed, etc….
According to the above information, you can choose the machine that suits you.
First, select the type of product and plastic material
Second, the mold can be placed on the machine, to determine the size of the tie, the height of the mold, the minimum size of the mold is appropriate.
Third, you can take out the product.
Switch trip is more than two times the height of the opening and closing of the product.
The jet’s journey is enough to spray the product.
Fourth, the clamping tonnage is determined by the plastic materials and products.
Fifth, the weight of the injection depends on the weight of the product and the mold cavity.
Sixth. Injection speed: thin-walled products always require high injection speed.

Compared with the traditional technology, Cn-moulding has higher precision injection molding and more perfect performance, which is often supplied to electronic information engineering, medical devices, packeging, cars, machinery, hardware, apparatus,timepiece industry, weapons and aerospace, etc. Therefore, it will become a revolution between parts molding and processing.

Custom injection molding -RIM technology

Custom injection molding in china

Custom injection molding in china

Custom Injection Molding in china for RIM

RIM (reaction injection molding), Chinese commonly known as reaction injection molding , is the late 1970s, first developed in Europe and America . Is different from the traditional injection molding and other molding process is a special process .
The principle is:
The two reaction materials ( polyurethane component and resin mixture ) with a stirrer were placed in a temperature-controlled feed tank , through accurate measurement , at high pressure into the mixing head at the start of injection , the mixing head of the valve to open , the reactants into the mixing chamber under pressure , speed fierce collision , near the atmospheric pressure and then flows into the mold , the exothermic chemical reaction in the mold to form a polyurethane polymer . This process can be simplified to : Store → Measurement → mixing → filling → curing → top out → post-processing.
RIM molding process is particularly suitable for large-scale ( large ) housing member .

PU resin first by Bayer (Bayer) (PU industry founder ) , Professor invented in 1937 , has been 70 years old .
Polyurethane with high strength, abrasion resistance , tear resistance, flex resistance, low temperature resistance and oil resistance, excellent chemical resistance and good blood compatibility , etc. , etc. . Polyurethane foam products made of resin , elastomers, coatings, adhesives , fibers, synthetic leather and other varieties of auxiliary surface material , which is widely used in transportation, electronics, shipbuilding , civil engineering , light industry and textile and other sectors , products and varieties yearly basis, in the material industry occupies important proportion of the current usage of the PU after PP, ABS, PVC. since the late 1930s since the advent of its applications continue to expand , production increased year by year , is developing very rapidly .
RIM process has the advantage ( own summary , we hope to supplement ) :
1 , shorten product development cycles , reduce product development costs
RIM technology to make product design becomes more free, more casual , and its expression on the product to better reflect the designer’s whim , and because of the low viscosity of the reaction material , good fluidity , can be very small in the case of pressure under molding complex parts ; due process of low pressure injection of RIM , low requirements of the mold , the mold is usually done using epoxy or aluminum material , so the cost is only a fraction of the equivalent injection mold , the processing cycle more is the injection mold can not match, the process is particularly suitable for short production and prototype production, can greatly shorten the product development cycle and saving development costs and speed to market share opportunities ;
2, can be molded article of a large area of good quality and the appearance and structure of the

RIM Procedure — Custom injection molding

RIM molding procedure of product size and stability , aesthetically pleasing ( up to Class A surfaces ) , impact resistance and good corrosion resistance ( up to PC / ABS performance ) , for forming a larger area of housing has unparalleled advantages, RIM product thickness range is very large, the same cross-section of molded parts,it  can vary between from 6mm to 28mm , which is the other process can not be compared , it can be integrally molded article thickness variations, in order to improve the quality of products reliability , good performance surface coating , which can meet different process requirements , formulated by adjusting the ratio of raw materials,it  can be made into a hard surface, such as density polyurethane foam structures of different products, to meet the diverse needs of customers ;

the product package inserts simple process
A variety of inserts can be placed in the injection mold before the RIM material , so that the RIM material in the molding process to complete the package insert , steel or aluminum structural frame , electronic sensors , circuit boards, batteries, antennas, magnets, glass, metal parts so you can use RIM technology package, thereby reducing or even eliminating secondary processing sectors , so you can : Protect your important and sensitive components from dust, oil , corrosive chemicals pollution ; make your product You can work in wet or even water ; increased intensity of your product and protect critical components from impact damage from impact or slow ; way so your products can be in more extreme environments.

Easy to mold paint spraying
In the RIM process, prior to injection can be coated with polyurethane paint and gel-coat in the mold . Gel-coat or polyurethane paint in the custom injection molding process and polyurethane materials combined into one, resulting in mold decoration finished parts , greatly reducing the cost and increasing the secondary painting after processing efficiency.
RIM technology because of its superior product performance are widely used in automotive parts and modification parts, engineering machinery covering parts , medical equipment , instrumentation , electronics, machinery and equipment covering parts , industrial parts , chemical components , sports and other fields, as alternative materials such as metal , has incomparable advantages and prospects .

want to know more for custom injection molding in china or custom plastic injection molding in china, visit our website or video at

Artical Reference page at : injection molding.html

Plastic Injection Moulding material —-PEI

Plastic Injection Moulding Product

Plastic Injection Moulding Product

PEI Characteristics  and application of plastic products

PEI: poly-ether imide with excellent mechanical properties, electric insulation properties, high radiation resistant, good resistance to low temperature and wear resistance, which is accessible via microwave.

As PEI both excellent high-temperature mechanical properties and wear resistance, steering valves can be used in the manufacture of water pipe valves and fittings. Due to its high flexibility and strength, heat resistance, is an excellent coating and film-forming material, and they can apply in the electronics industry coatings and thin films.

Main characteristics of continuous operating temperature range (long-term exercise -200–170) glass transition temperatures and thermal denaturation temperature close, up to 330 degrees at low/high temperature melting point has maintained high mechanical strength, high hardness, high outstanding resistance to creep resistance, good toughness of precipitation.

So PEI widely used, mainly used in the electronics industry: Shell connectors, General and micro-relays, circuit boards, coils, soft circuits, secret mirror, high precision optical components, high-temperature insulating Board. Automotive industry: connectors, high power lights and indicator lights, control of vehicle cabin external temperature sensors, control of air and fuel mixture temperature sensor, medical equipment and so on.

This our company’s production of PEI products :

Our company specialized in plastic injection moulding mold design, production and plastic injection molding production.
Materials include not only the commonly used ABS,PP,PC,PA and so on, but also covers special plastics such as PPEK,POM,PPT,PEI and so on.

China Forefront Plastic Injection Moulding Company

If you are looking for a company offering quality and precision manufacturing in the field of plastic injection moulding, Cnmoulding is at your disposal. Being at the forefront of the China market for plastic mouldings, we have developed our experience in the design, creation, innovation, manufacturing and delivery of plastic injection mouldings for a variety of purposes.

Our precision manufactured plastic parts and components are used throughout a host of industry sectors.

Our efforts as a team in the field of initial concept design and in the manufacturing stage are the guarantee of quality injection moulding, and we can offer you quality in the preparation of CAD drawings, research and design, tooling, etc – all your needs for plastic injection moulding. With more than twenty years experience we are able to deal with all volumes, sizes and shapes

panels for cars, mechanical parts, as well as small plastic mouldings such as bottle caps, spools, combs, etc.
In special plastic injection moulding materials if you face any technical problems in product development, Reference at for solution

Gas assistant injection molding china

Gas assistant injection molding china

Gas assistant injection molding technology

Application prospect  gas assistant injection molding china 

Gas-assisted injection molding china technology is widely developed . Since 1990, as a new type of technology, in order to overcome the limitations of traditional injection molding, plastic injection engineering community is of general concern. The use of gas-assisted technology, improve product accuracy, surface quality, to solve large size and wall thickness varied deformation of the product, improve product strength, reduce stress, save plastic materials and greatly simplify mold design, widely used in automotive, household appliances, office supplies , household products and many other fields. It is called the second revolution of the plastic injection molding china industrial. Process simulation of gas assisted injection molding with CAE software, help us to understand the melt filling in injection molding process, the gas-assisted filling, gas protection pressure molding process, to avoid the injection melt insufficient, the gas pressure is too large, cavitation, blowing wear surface depression occur to determine the the melt gate, gas inlet position, the runner dimensions airway size optimization and airway reasonable arrangement, material selection, process conditions set, And through the analysis of the calculation results, determine a set of the best program to ensure the test model success. In recent years We have successfully passed CAE analysis software to assist injection molding of home appliances and automotive parts, and achieved good results.

Gas-assisted  control 2 ways of injection molding china company

Gas assisted injection molding molten resin injection, gas injection, gas holding pressure, gas recovery, part ejection, and several major steps.The molten resin is injected into the mold cavity through the gate , and then inject a constant pressure of an inert gas (usually nitrogen), The resin is produced by the gas pressure, and is filled to the various parts of the mold cavity. So that the plastic part to finally form a hollow section while maintaining the full shape. And from the interior of the resin packing, the gas pressure becomes the holding pressure. Gas emissions occur at the end of the cooling mold. Compared with the conventional injection molding process, a gas-assisted filling stage, and the packing stage holding pressure by air pressure. Holding pressure, can reduce stress and prevent Warp products. Due to the pressure exerted by the gas can effectively pass, The internal surface of the product can be ensured during the cooling process to compensate for the volume shrinkage. And also to avoid the deformation when part ejection. Using gas assisted injection molding, is controlled by the amount of plastic to control the injection cavity articles the hollow ratio and the shape of the airway. Gas-assisted injection molding pressure control method and volume control method are two ways.

2 gas-assisted for china injection molding and china mold maker technology features

  • 2.1 is capable of forming wall thickness difference larger products and complex three-dimensional hollow products

Gas-assisted technology into the airway wall thickness at the hollowed design, thus ensuring the thickness difference the larger molding quality of the products, the use of gas-assisted technology, but also to simplify the structure of the products. Parts due to the large wall thickness difference had to be divided into several parts, molding and then together, forming one gas-assisted technology.

  • 2.2 injection pressure is low

Gas from the gate to the end of the current to form a continuous flow passage, no pressure loss can be realized in low-pressure injection molding, therefore, the residual stress is smaller parts, warpage deformation is small, dimensionally stable.

  • 2.3 to eliminate sink marks, improve the quality of the product surface

In the the gas packing process, the contraction of the plastic secondary penetration by the gas to be compensated, so that the parts will not sag In addition, the use of gas-assisted injection molding, the thicker part of the products can be hollowed out to reduce or even eliminate sink marks.

In addition, to enhance the strength and stiffness, but also save materials, shorten the molding cycle.

Custom injection moulding process

custom injection molding
Custom injection moulding  is a process of shaping plastic by melting it and injecting it into a predesigned mold. The process was first designed in the 1930s and was originally based on metal die casting designs. It offers many advantages to alternative manufacturing methods, including minimal losses from scrap (since scrap pieces can be melted and recycled), and minimal finishing requirements. This process differs from metal die casting in that molten metals can simply be poured; plastic resins must be injected with force.

The china custom injection moulding process uses large injection molding machines, which advance the resins through six major processes to produce everything from computer parts to plastic Halloween spiders. Although this machine is a complex piece of equipment, custom injection moulding will consists of two basic elements: the injection unit and the clamping unit. The process starts with a mold, which is clamped under pressure to accommodate the injection and cooling process. Then, pelletized resins are fed into the machine, followed by the appropriate colorants. The resins then fall into an injection barrel, where they are heated to a melting point, and then injected into the mold through either a screw or ramming device.Then comes the dwelling phase, in which the molten plastics are contained within the mold, and hydraulic or mechanical pressure is applied to make sure all of the cavities within the mold are filled. The plastics are then allowed to cool within the mold, which is then opened by separating the two halves of the mold. In the final step, the plastic part is ejected from the mold with ejecting pins. The completed part may contain extraneous bits called runners, which are trimmed off and recycled. The entire process is cyclical, with cycle times ranging from between ten and 100 seconds, depending on the required cooling time.

Custom injection moulding process requires some complex calculations. Every different type of resin has a shrinkage value that must be factored in, and the injection molds must compensate for it. If this value is not precisely determined, the final product will be incorrectly sized or may contain flaws. Typically, this is compensated for by first filling the mold with resin, holding it under pressure, and then adding more resin to compensate for contraction. Other complications may include burned parts resulting from the melt temperature being set too high, warpage resulting from an uneven surface temperature, or incomplete filling due to a too slow of an injection stroke.

China custom injection moulding can be surprisingly expensive, sometimes upward of $100,000 US Dollars (USD). If the desired part quantity is great enough, however, the mold cost becomes relatively insignificant, and the resulting plastic parts are very reasonably priced. Some molds are made with more than one cavity; these multicavity molds cost more than their single cavity counterparts, but due to increased production efficiency, the cost per part is minimized.

China custom injection moulding method can be used with a variety of plastic resins. The most popular resins for this type of molding include polypropylene (PP), polyethylene (PE), and ABS. Each has its own set of advantages and disadvantages, and they are chosen based on the desired characteristics of the final part.