Here are 15 examples of common molding issues that occur during an initial mold trial. Jim Fattori. Injection molders quote or estimate a job based on six primary factors: part weight, material cost, machine size, cycle time, labor requirements and packaging. The material and packaging costs are relatively easy to obtain from suppliers, which makes them fixed values—not estimates. Thanks to solid modeling software programs, part weight is also a fixed value, based on the models volume and the density of the material.

These three estimates typically determine if you are going to make money or lose your shirt. He, or she, base them on the mold performing as it should—in the correct machine, at the anticipated cycle time, and with the expected number of operators required.

Cycle time, machine size and labor requirements are the big three cost variables—that can be controlled by the mold design. They all relate to the mold construction, but not the molding process. Most of these checklists address the function of the part, or the repeatability of the mold and machine to make the part. Very few checklists are geared towards preventing mold-design problems that arise at the initial mold sampling. What can be done if this or that happens during the initial mold trial?

Many of them are avoidable or correctable with a proactive checklist.

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The machine tonnage, tiebar spacing and shot size were all taken into account during the mold design phase. The processor starts to dial in the machine settings. The first thing he encounters is the 4-in.

The mold has an eight-drop hot-runner system with 12 heat zones. The processor has no idea what zone controls which component. He turns the controller on. The zones that come up to heat slowly are for the manifold. The zones that come up to heat quickly are for the cavities.

If so, do the zone numbers correspond with the cavity numbers? The mold has a stripper-plate ejection system. The processor can do the math based on the barrel diameter and the volume, or he can simply take an air-shot and weigh it. The cavities are out of balance. The four inside cavities fill first and the four outboard cavities are short.What is a injection molding?

Injection Molding

How does it work and what is it used for? In this section, we answer these questions and show you common examples of injection molded parts to help you familiarize yourself with the basic mechanics and applications of the technology. Injection molding is a manufacturing technology for the mass-production of identical plastic parts with good tolerances.

In Injection Molding, polymer granules are first melted and then injected under pressure into a mold, where the liquid plastic cools and solidifies. The materials used in Injection Molding are thermoplastic polymers that can be colored or filled with other additives. Almost every plastic part around you was manufactured using injection molding: from car parts, to electronic enclosures, and to kitchen appliances. Injection molding is so popular, because of the dramatically low cost per unit when manufacturing high volumes.

Injection molding offers high repeatability and good design flexibility. The main restrictions on Injection Molding usually come down to economics, as high initial investment for the is required. Also, the turn-around time from design to production is slow at least 4 weeks.

mold design requirements

Injection molding is widely used today for both consumer products and engineering applications. Almost every plastic item around you was manufactured using injection molding.

Basics of Injection Molding Design

But compared to other technologies, the start-up costs of injection molding are relatively high, mainly because custom tooling is needed. All thermoplastic materials can be injection molded. Some types of silicone and other thermoset resins are also compatible with the injection molding process. The most commonly used materials in injection molding are:. InJohn Wesley Hyatt invented celluloid, the first practical artificial plastic intended to replace ivory for the production of Early injection molding machines used a barrel to heat up the plastic and a plunger to inject it to the mold.

In the mid s, the invention of the reciprocating screw single-handedly revolutionized the plastics industry.

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The reciprocating screw solved key issues with uneven heating of the plastic that previous systems faced, and opened up new horizons for the mass production of plastic parts. Recently, the demand of biodegradable materials is increasing for environmental reasons. In this section, we examine the purpose of each of these systems and how their basic operation mechanics affect the end-result of the Injection molding process.

Watch a large injection molding machine in action while producing 72 bottle caps every 3 seconds in the video here:. The purpose of the injection unit is to melt the raw plastic and guide it into the mold. It consists of the hopperthe barreland the reciprocating screw. The mold is like the negative of a photograph: its geometry and surface texture is directly transferred onto the injection molded part. This is due to the high level of expertise required to design and manufacture a high-quality mold that can produce accurately thousands or hundreds of thousands of parts.

Molds are usually CNC machined out of aluminum or tool steel and then finished to the required standard. Apart from the negative of the part, they also have other features, like the runner system that facilitates the flow of the material into the mold, and internal water cooling channels that aid and speed up the cooling of the part.

Learn more about CNC machining. Read the complete engineering guide Recent advances in 3D printing materials have enabled the manufacturing of molds suitable for low-run injection molding parts or less at a fraction of the cost.Learn More.

Once done, you can build an injection mold to meet the product specifications. The role of the Design Engineer is critical in this process. They assess the part design and make modifications and recommendations based on key product requirements including product usage and function. The engineer will need to know:. A plastic injection mold design is built with these criteria in mind. Mold cavities, vents and gate placement will vary based not only on the part design but the type of resin as well.

Taking all of these manufacturing factors into account is a challenging task and one that requires a strong knowledge base, not only of mold design but the injection molding process as well.

mold design requirements

We took some time recently to talk to one of our Design Engineers, Mike Baranoski, a Rodon employee for 24 years.

Mike and his wife have three boys. Their middle son, Matt, will complete this year in Brazil as a member of the U. Olympic Cycling team. We asked Mike to give his perspective on the plastic design process:.

My background was in tool and mold building. In the years following, I changed jobs several times to try to get as much experience as I could.

I will have been at Rodon for 25 years early next year. The first thing I do when I receive a new part or concept is to make sure that the part is moldable.

7 Ways to Save on Injection Molding

I recommend changes to the customer to make the part and tool as simple and robust as I can. The simpler the tool, the less they will have to pay for it. The stronger the tool is made, the less down time Rodon will have, and the more dependable part delivery the customer will have.

We have had several design challenges over the years. Most are solved by analyzing the parts real function and modifying it to achieve those requirements while making it mold friendly. The common problems are always gating, venting and cooling.

Each can be changed or altered as needed to produce a part that will meet the needs of our customers. The demand requirements of plastic parts have increased over the years, and so has the selection of materials that we use. I was the tool shop foreman before I moved into design. That gives me an invaluable view of tooling and its design. I constantly alter tool designs to make it how I would like it if I were building it myself. I was also able to see firsthand out in the shop what concepts failed and what concepts ran for years of maintenance-free operation.

Eventually not only will you be able to print a working model of your part but you will be able to print the mold to manufacture high-volume injection mold parts. They already have a hybrid process that combines 3D laser sintering and high-speed milling to produce an accurate cavity.

The future is very exciting when it comes to this kind of innovative thinking. We have double checks set up along the way.Minnesota Rubber and Plastics' custom-molding capabilities encompass all three processes — transfer, compression and injection molding. We select from among these methods based on a number of key factors, including: the size and shape of the part, the hardness, flow and cost of the material, and the anticipated number of parts to be produced.

The compression molding process is not unlike making a waffle. A surplus of material must be placed in the cavity to ensure total cavity fill. Heat and pressure are applied, causing the compound to flow, filling the cavity and spilling out into overflow grooves.

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Compression molding is often chosen for medium hardness compounds — in high volume production, or applications requiring particularly expensive materials. The overflow, or flash, created by larger diameter parts is of particular concern when using the more expensive compounds. Compression molding helps to minimize the amount of overflow. The pre-load, however, can be difficult to insert in a compression mold of more complex design, and the compression molding process does not lend itself to the material flow requirement of harder rubber compounds.

Applications range from simple o-ring drive belts to complex brake diaphragms with diameter of more than Transfer molding differs from compression molding in that the material is placed in a pot, located between the top plate and plunger. The material is squeezed from the pot into the cavity through one or more orifices called gates, or sprues. Injection molding is normally the most automated of the molding processes.

The material is heated to a flowing state and injected under pressure from the heating chamber through a series of runners or sprues into the mold. Injection molding is ideal for the high volume production of molded rubber parts of relatively simple configuration.

Molding Processes Minnesota Rubber and Plastics' custom-molding capabilities encompass all three processes — transfer, compression and injection molding. Compression Molding The compression molding process is not unlike making a waffle.

Transfer Molding Transfer molding differs from compression molding in that the material is placed in a pot, located between the top plate and plunger. Injection Molding Injection molding is normally the most automated of the molding processes.Adhering to some basic rules of injection molded part design will result in a part that, in addition to being easier to manufacture and assemble, will typically be much stronger in service.

Designing plastic parts is a complex task involving many factors that address a list of requirements of the application. How the molten plastic enters, fills, and cools within the cavity to form the part largely drives what form the features in that part must take.

Dividing a part into basic groups will help you to build your part in a logical manner while minimizing molding problems. As a part is developed, always keep in mind how the part is molded and what you can do to minimize stress.

Plastic injection molding is the preferred process for manufacturing plastic parts.

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Injection molding is used to create many things such as electronic housings, containers, bottle caps, automotive interiors, combs, and most other plastic products available today. It is ideal for producing high volumes of plastic parts due to the fact that several parts can be produced in each cycle by using multi-cavity injection molds.

Injection Molding Design Guidelines and Principles

Some advantages of injection molding are high tolerance precision, repeatability, large material selection, low labor cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are expensive upfront tooling investment and process limitations. There are tens of thousands of different materials available for injection molding.

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The available materials mixed with alloys or blends of previously developed materials means that product designers can choose from a vast selection of materials to find the one that has exactly the right properties.

Materials are chosen based on the strength and function required for the final part; but also each material has different parameters for molding that must be considered. Injection molding machines, also known as presses, consist of a material hopper, an injection ram or screw-type plunger, and a heating unit. Molds are clamped to the platen of the molding machine, where plastic is injected into the mold through the sprue orifice.

Presses are rated by tonnage, which is the calculation of the amount of clamping force that the machine can exert. This force keeps the mold closed during the injection molding process. Tonnage can vary from less than 5 tons to 6, tons, although the higher tonnage presses are rarely used. The total clamp force needed is determined by the projected area of the custom part being molded. This projected area is multiplied by a clamp force of from 2 to 8 tons for each square inch of the projected areas.

If the plastic material is very stiff, it will require more injection pressure to fill the mold, thus more clamp tonnage is needed to hold the mold closed. The required force can also be determined by the material used and the size of the part with larger plastic parts requiring higher clamping force. The mold or die refers to the tooling used to produce plastic parts in molding.

Traditionally injection molds have been expensive to manufacture and were only used in high-volume production applications where thousands of parts were produced. The choice of material to build a mold from is primarily one of economics. Steel molds generally cost more to construct but offer a longer lifespan that will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel molds are less wear resistant and are primarilly used for lower volume requirements or larger components.

The hardness of the pre-hardened steel measures typically on the Rockwell-C scale. Hardened steel molds are heat treated after machining, making them superior in terms of wear resistance and lifespan.

Aluminum molds cost substantially less than steel molds, and when higher grade aluminum such as QC-7 and QC aircraft aluminum is used and machined with modern computerized equipment, they can be economical for molding hundreds of thousands of parts.

Aluminum molds also offer quick turnaround and faster cycles because of better heat dissipation.Communicating with the manufacturing team, learning and understanding manufacturing techniques and applying that knowledge within the design is critical. Under design issues can result in very serious consequences and over design results in high cost. The challenge is designing in high speed performance and long low maintenance mold life.

In order to maintain a mold delivery schedule we must maintain deliveries in our mold design area as well as the manufacturing area. Setting milestone schedule goals, measuring against those goals and working corrective actions when issues arise to get the schedule on track is extremely important. The core need here is for good consistent productivity, communication, and on-time mold design delivery.

Communicate risk to design delivery and initiate and assist in implementation of corrective action plans to get back on track when there are delivery issues. The following is a list of critical design requirements which the designer is responsible to document using the KOW checklist:.

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Review customer data, 2D and 3D for moldibility and critical design requirements. Molding machine specifications and customer interface requirements mounting method, part removal, etc.

Mold cavitation and desired molding cycle Customer production requirements. Engineering calculations which can include cooling, de-molding, hydraulics, etc. Communicate status and goals daily and escalate information issues to resolve as quickly as possible. The critical design milestones that require target dates are as follows:. When design milestone dates are at risk communicate with the design manager and develop and implement corrective action plans.

This is to be reviewed with the mold design manager within 3 days from KOW meeting. Design engineer will make changes based on this review and proceed with the preliminary design.

mold design requirements

Once complete, designer to update design schedule and check-off operation. Drawings showing plan views and proper section views of the mold are also required for the internal preliminary review.

Note: Full scale drawings are preferred. Based on review, engineer will make the required changes and if required have an additional review s with the team.

The preliminary design checklist must be completed by both the mold design engineer and program manager at the customer review. Any change requests must be reviewed internally and then made to the mold design. Designer is responsible to make sure all BOM information is accurate for quantities including sparesmaterials and sizes. Design engineer is to review manufacturing requirements for roughing and supply required IGES files. Design engineer to notified design manager when this is complete.

Mold designer to go thru the design checklist. The following functional checks need to be reviewed:. Do we have proper clearances between the cooling lines and near by hole features? Design engineer is responsible to review all detailed drawings for proper dimensioning and stack up tolerances.Get a practical and comprehensive look at injection mold design and learn to contribute to the overall success of projects. Receive a unique blend of detailed mold design concepts set forth in the context of the whole design process, and on the final day, participate in that process.

For April, sessions: This course will be offered online with synchronous live lecture and discussion from 8ampm. For additional details or questions, please contact Marcia Gabriel at gabrielm uwm.

This course can be applied to the Plastics Technology Certificate. John Vosmeier. He has worked with Custom and Proprietary molders over Anyone responsible for procuring, evaluating, building or designing injection mold tools, including tooling engineers, buyers, toolmakers, mold designers, product designers, managers and molders. Instructor: John Vosmeier.

Registration Deadline: Mon. Plastic Injection Mold Design Basics Get a practical and comprehensive look at injection mold design and learn to contribute to the overall success of projects.

Understand mold design concepts Avoid costly mistakes Specify and evaluate your purchases of molds. Introduction and Overview The Anatomy of a Mold Mold Types Stripper plate molds Unscrewing molds Quick change molds Hot runner molds Shuttle molds Basic Mold Construction Use and placement of bolts and dowels Major suppliers and differences between them How to specify and order mold bases and components Common Components and their Function Leader pins, return pins, support pillars, rest buttons, etc.

The Molding Press How the mold interfaces with the press Horizontal and vertical clamp Shuttle and rotary presses Plastic Resin Fundamentals Amorphous and semi-crystalline Basic properties and how they affect the mold design Shrink How to use shrink to your advantage Factors that affect shrink and warp Plastic Product Design Fundamentals Common errors What the mold designer needs to look for in a product design Sprue, Runner and Gate Common gate design errors Runner sizing guidelines Runner pullers Ejection Determining ejector place Pin orientation methods Knock-out patterns Return pins and springs Basic Mold Inserting Solid vs.

Meet Instructor John Vosmeier. Sessions All sessions are Face-to-Face unless otherwise noted.

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