The Importance Of Plastic Parts Design

Injection moulding is popular manufacturing method because of its high-speed production capability. Performance of plastic part is limited by its properties which is not as strong as metal. A well-designed plastic parts means that it was taken through many steps to solidify the mold you wish to create. It’s hard to change the specs and variables of a plastic part towards the end of the plastic part design process.Not only will you have to reassemble machine parts and measurements, it will be more time consuming and will cost more to fix the issues after production.Making changes during the design stage is relatively inexpensive. With today’s CAD software, being able to visualize, test, and change designs has never been easier.

These are just a few of the questions that should be asked during the plastic part design process.

• The Cost of Change
• A well designed plastic part has many variables that need to be taken into account.
• How will the mold come together?
• Can the part be ejected from the injection mold?(If the tools and machine aren’t sized correctly, it may be hard to eject the mold.)
• Are the walls too thick or too thin?(If the wall selections are too thin, it may break off in the tool and not fill correctly. Too thick of wall sections will take longer to cool and solidify before ejecting the mold, resulting in warped or cracked products.)

An improper design technique, if carried all the way to production, can have a negative result on the overall quality or appearance of the injection molded piece. The cost to fix issues observed after production are not only expensive but also time consuming.

It is important however to look beyond just the question “Can this part be injection molded successfully?” While this is an important aspect of the design, we must also be mindful of manufacturing costs. Because the tooling cost is closely related to the product design, it is crucial to have an understanding of the mold making process even during the design stages. Plastic part design can greatly vary the overall costs and in some cases out-price the project. Implementing cost saving design features while maintaining design intent, or just optimizing the design for injection molding will save you money and make for a more robust design. Jingwei industry has served the injection molding industry for over 20 years and has a team dedicated to providing you with the most cost effective solutions for design and manufacturing.

Design points before production:

• Select the proper material for the building tools. The coefficient of thermal expansion must be taken into consideration; large differences in material and size can damage and uneven the components.
• Be sure the runner system is balanced. Unbalanced runner systems can cause filling disturbances and inefficient tool running.
• Choosing a gate design is similar to having a balanced runner system. The gate is the area where the polymer transits from the runner to the part. If this is wrong, the gate could cause restrictions, incorrect polymer flow, turbulence, or other defective filling issues.

Contact an experienced Chinese plastic injection molding company, Jingwei industry via info@jweimolding.com

Plastic Injection Molding Glossary

 

Below are words commonly used in the plastic injection molding industry:

Additive Manufacturing – The technical term for 3D printing -- the process of manufacturing a three-dimensional object by placing layer on top of layer -- based on a CAD model.

Blow Molding – A technique in which plastic is forced to take on the shape of a mold cavity by way of a hollow plastic tube applying internal pressure with air.

Blushing – The whitening of plastic in areas that come under high stress.

Casting – Injecting liquid plastic into a mold without using pressure to form solid o-hollow articles.

Cavity – A hollow part of a mold that forms the outer part of a plastic-molded object.

Curing – Using heat, chemicals or radiation to make a polymer more stable and functional by changing its physical properties.

Degradation – A change in physical properties of plastic resulting from light exposure, heat, exposure to oxygen and general weathering.

Extrusion – Forcing molten plastic through a die in order to form continuous shapes.

Fabricating – The use of various manufacturing methods to create plastic products -- examples of fabrication processes include: cutting, tapping, fastening and punching such plastics as sheets, tubes, rods and more.

Gate – Molten resin flows through the gate in order to get from the runner to the cavity of the mold.

Impact Resistance – The measure of how much a plastic item can withstand high-speed stresses.

Injection Molding – The process of creating plastic parts and components by way of heating granular or powdered plastics and then forcing the liquid into a mold.

Insert Molding – The process of forming an object by molding plastic around metal inserts.

Land Area – The part of a mold where surfaces come in contact with one another when the mold is closed.

Low Temperature Flexibility – The ability of plastic to withstand fracturing at low temperatures.

Mar Resistance – A glossy plastic’s resistance to damage caused by abrasion.

Masterbatch – Within a polymer base -- the concentration of pigments, fillers, additives and other substances.

Melt Flow – The viscosity of a polymer based on the polymer’s weight when extruded under certain pressure and temperature -- varying by specific polymer.

Memory – A plastic article’s tendency to revert to previous dimensions based on earlier stages of manufacturing.

Metalizing – Covering or coating any plastic item with metal.

Mineral Reinforcements – Inorganic substances such as clay, talc or mica used as filler in plastics.

Mold Frame – The steel plates that comprise the components used in molding -- mold frames typically include: cores, runner systems, cavities, cooling systems and ejection systems.

Polymer – Organic compounds of high-molecular weight -- naturally occurring or synthetically made.

Sink – Imperfections such as dimples that occur as plastic cools at different rates along the surface.

Splay – Streaks occurring as the result of moisture in resin.

Sticking – A complication during ejection, during which a part is lodged in half of a mold.

Tear Strip – A removable feature that creates a crisp end of a molded part.

Warp – Curving or bending that results as a part cools and shrinks at varying rates along a surface

Jingwei industry has served the injection molding industry for over 20 years and has a team dedicated to providing you with the most cost effective solutions for design and manufacturing.Contact us via info@jweimolding.com

Injection molding is a complex process

Injection molding is a widely used process for high volume production of thermoplastic resin parts. It can produce complex parts with different combination of plastics and fillers and has a high efficiency ratio between applied material and the end product.

Despite major advantages of injection molding, there are significant difficulties in controlling quality of the molded part. These difficulties arise not only from the complex dynamics of the process and unpredictable behavior of the material under temperature-pressure fluctuations, but also from the lack of consistent relationships between the material properties, machine parameters, mold geometry and molded part quality. There are several sources of variation in the injection molding process which include material properties, process machinery, mold design, environmental fluctuations, and human interaction. If these factors had precisely defined and deterministic effects on the process, the quality of the molded part could be easily controlled. However, there are many interactions between stochastic factors, resulting in frequent irregularities in process parameters so the ideal state of constant quality does not exist. Examples of such irregularities include mold and melt temperatures that can drift from their set values, changes in polymer properties from batch to batch, and the machine and tool performance, which alter as they wear. Besides these major factors there exists small natural fluctuations making the process even more unpredictable.

There are several different approaches to quality control and process optimization that are used in industry today,such as expert systems, continuous process control, regression modeling, and design of experiments. Unfortunately, none of these approaches deliver 100% quality assurance. Difficulties in regulation arise mainly from non-linear character of the process and interactions between inputs that make the relationships between machine parameters and part quality not obviously defined. At the same time, the number of variables adds difficulty in evaluation of the significant parameters. Thus, a more capable quality control system requires a process model that not only describes the relationship between the process parameters and the resulting part quality, but is also capable to learn and express the process nonlinearities and complexities. Because of the stochastic correlations between the process parameters and characteristics of part quality, such a model should also be adaptable to the changing process conditions.

To overcome the difficulty require the engineers have wide knowledge and humble attitude. It is a course of researching, and should be complex.

SO,injection molding is a complex process!

Contact an experienced Chinese plastic injection molding company, Jingwei industry via info@jweimolding.com

How much does plastic injection molding cost?

Plastic injection molding is the most commonly used process in the factories as its demand in the market is quite high and is rapidly rising also with the each passing year. Because of its cheaper cost and fast manufacturing to gives the desired shaped results, it is very renowned among the people.

The manufacturing of an injection mold could possibly be the greatest expense a new product faces in the development cycle.The most common question we hear from designers and product engineers is, "How much will a plastic injection mold cost to make my product?"

Many factors play roles and directly affect the cost incurred to create an injection mold for your custom parts. In any case, a reliable injection molder should be able to provide an accurate estimate quickly from either a 3D CAD file, sketch or the general dimensions of your product.

Material cost

The material cost is determined by the weight of material that is required and the unit price of that material. The weight of material is clearly a result of the part volume and material density; however, the part's maximum wall thickness can also play a role. The weight of material that is required includes the material that fills the channels of the mold. The size of those channels, and hence the amount of material, is largely determined by the thickness of the part.

Production cost

The production cost is primarily calculated from the hourly rate and the cycle time. The hourly rate is proportional to the size of the injection molding machine being used, so it is important to understand how the part design affects machine selection. Injection molding machines are typically referred to by the tonnage of the clamping force they provide. The required clamping force is determined by the projected area of the part and the pressure with which the material is injected. Therefore, a larger part will require a larger clamping force, and hence a more expensive machine. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as clamp stroke, platen size, and shot capacity.

The cycle time can be broken down into the injection time, cooling time, and resetting time. By reducing any of these times, the production cost will be lowered. The injection time can be decreased by reducing the maximum wall thickness of the part and the part volume. The cooling time is also decreased for lower wall thicknesses, as they require less time to cool all the way through. Several thermodynamic properties of the material also affect the cooling time. Lastly, the resetting time depends on the machine size and the part size. A larger part will require larger motions from the machine to open, close, and eject the part, and a larger machine requires more time to perform these operations.

Tooling cost

The tooling cost has two main components - the mold base and the machining of the cavities. The cost of the mold base is primarily controlled by the size of the part's envelope. A larger part requires a larger, more expensive, mold base. The cost of machining the cavities is affected by nearly every aspect of the part's geometry. The number of cavities you incorporate into your mold will directly correlate in molding costs. Fewer cavities require far less tooling work, so limiting the number of cavities in-turn will result in lower initial manufacturing costs to build your injection mold.

The quantity of parts also impacts the tooling cost. A larger production quantity will require a higher class mold that will not wear as quickly. The stronger mold material results in a higher mold base cost and more machining time.

One final consideration is the number of side-action directions, which can indirectly affect the cost. The additional cost for side-cores is determined by how many are used. However, the number of directions can restrict the number of cavities that can be included in the mold. For example, the mold for a part which requires 3 side-action directions can only contain 2 cavities. There is no direct cost added, but it is possible that the use of more cavities could provide further savings.

Contact an experienced Chinese plastic injection molding company, Jingwei industry via info@jweimolding.com

Plastic Injection Moulding Process Cycle

Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. A wide variety of products are manufactured using injection molding, which vary greatly in their color,size, complexity, and application. The injection moulding process requires the use of an injection molding machine, raw plastic material, and a mold. The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part. The process cycle for injection moulding is very short, typically between 2 seconds and 2 minutes, and consists of the following four stages:

Clamping - Prior to the injection of the material into the mold, the two halves of the mold must first be securely closed by the clamping unit. Each half of the mold is attached to the injection molding machine and one half is allowed to slide. The hydraulically powered clamping unit pushes the mold halves together and exerts sufficient force to keep the mold securely closed while the material is injected. The time required to close and clamp the mold is dependent upon the machine - larger machines (those with greater clamping forces) will require more time. This time can be estimated from the dry cycle time of the machine.
Injection - The raw plastic material, usually in the form of pellets, is fed into the injection molding machine, and advanced towards the mold by the injection unit. During this process, the material is melted by heat and pressure. The molten plastic is then injected into the mold very quickly and the buildup of pressure packs and holds the material. The amount of material that is injected is referred to as the shot. The injection time is difficult to calculate accurately due to the complex and changing flow of the molten plastic into the mold. However, the injection time can be estimated by the shot volume, injection pressure, and injection power.
Cooling - The molten plastic that is inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. As the plastic cools, it will solidify into the shape of the desired part. However, during cooling some shrinkage of the part may occur. The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage. The mold can not be opened until the required cooling time has elapsed. The cooling time can be estimated from several thermodynamic properties of the plastic and the maximum wall thickness of the part.
Ejection - After sufficient time has passed, the cooled part may be ejected from the mold by the ejection system, which is attached to the rear half of the mold. When the mold is opened, a mechanism is used to push the part out of the mold. Force must be applied to eject the part because during cooling the part shrinks and adheres to the mold. In order to facilitate the ejection of the part, a mold release agent can be sprayed onto the surfaces of the mold cavity prior to injection of the material. The time that is required to open the mold and eject the part can be estimated from the dry cycle time of the machine and should include time for the part to fall free of the mold. Once the part is ejected, the mold can be clamped shut for the next shot to be injected.
After the injection molding cycle, some post processing is typically required. During cooling, the material in the channels of the mold will solidify attached to the part. This excess material, along with any flash that has occurred, must be trimmed from the part, typically by using cutters. For some types of material, such as thermoplastics, the scrap material that results from this trimming can be recycled by being placed into a plastic grinder, also called regrind machines or granulators, which regrinds the scrap material into pellets. Due to some degradation of the material properties, the regrind must be mixed with raw material in the proper regrind ratio to be reused in the injection moulding process.

Contact an experienced Chinese plastic injection molding company, Jingwei industry via info@jweimolding.com

How to do business with a Chinese plastic injection molding company

Obviously there are a lot of benefits working with a Chinese plastic injection molding suppliers. They are professional, enthusiastic, hard-working, high quality and low price.

There are still many negative comments about Chinese suppliers. Many questions may arise by miscommunication and culture differences. Here we provide some suggestions for your reference when doing businsess with a Chinese injection molder.

Detail your requirement as detailed as possible

Before you start working with a Chinese injection molder, you’d better to describe your technological requirements clearly and double check with them. It is human nature to shirk theire reponsibility. Many problems come from inadequate communication, especially you are talking with a Chinese sales who are not good at both English and the technology. They are more like a translator. So it it depenent on the buyer to specify the things.

Be aware of the extreme low quotation

The buyers will get tons of promotional letters from everywhere of China. Some suppliers can quote an extreme low price for their injection molding service. Don’t trust them. They may use the very low quality material. Maybe you can get the good sample, after you place the order and pay the money, it is too late.

Try to know more Chinese culture

You should know some merit and weakness of Chinese people. The Chinese are hospitable, dedicated and hard-working, but not good at expression. Sometimes, they are afraid to let customers know the problems which may make the clients angry according to their speculation. If you know the character, you may understand how to avoid the potential problems.

Contact the experienced Chinese plastic injection molding companies, Jingwei industry via info@jweimolding.com

How to reduce the cost of your injection mould

Injection Mould is the biggest cost of manufacturing a plastic part. Here we share some advices about reducing the cost of mould making.

1.Reasonable Part Design

Part design is the most important factor to impact the cost of mould. Bad design is diaster for the mould maker. In many cases, the cost of Plastic Injection Mould  increases largely due to an unneccessary undercut design. It is benefit for a product designer to know more knowledge of mould. Adequate communication between designers and engineers can help to reduce the cost of mould making.

2.Design Alteration

We often meet the circumstances that we get the notice of design changing after we already confirm the structure of mould and purchase the mould base. It is ok for the tiny variety of design. But many times the change would be not small. Then we have to overthrow the confirmed structure of mould and redesign it. It is better to do more test of prototypes before starting the mould making.

3.Mould Design

For a experienced mould design team, there are many fixed structure of mould for some specific products. Their
experience can reduce the risk of failure and reduce the cost of mould. It is important for the product designer to
reach the right suppliers.

4.Number of mould trials

Before start up of mass production, the manufacturer would do some sample runs to test the mould performance, it was named mould trial. The higher number of mould trial, the higher cost of mould. Generally speaking, the ideal mould shop should have an experienced engineer to do the test.

5.Mould material and standard components

The high quality mould dependent on the high quality mould material and standard components. Some cheap material and components may result in many problems when manufactring the plastic parts.

Contact an experienced Chinese plastic injection molding company, Jingwei industry via info@jweimolding.com