A fully described plastic part is the most crucial information for a mold build project. An incomplete part drawing can create countless problems in the mold design process, waste a lot of precious time and cause numerous issues when the mold is completed and commissioned at the customer’s facility.
Spending extra time at the beginning of the mold design project to create a fully described part, which considers all aspects of the mold design, can save tens of thousands of dollars for the moldmaker, and hundreds of thousands of dollars for the molder and OEM.
While creating the plastic part drawing, the designer has the best opportunity to decide on the most suitable design for the mold and/or to make suggestions on how the product design might be modified to improve productivity and simplify the mold design; in turn, simplifying the mold design reduces mold costs. Cost and opportunity for change over the time of a mold build project.
Making improvements, revisions and selections at the outset of a project offers the most significant potential to affect the final outcome, including the part cost. Once the mold design concept has been agreed upon, and as engineering of the mold progresses, the opportunity to make conceptual changes or improvements diminishes and any costs associated with it will increase. By the time the project reaches completion, the opportunity to make changes is low, and any costs could add up to 150 times the cost of a change in the design phase!
Key Components of a Plastic Part Drawing
At the beginning of a mold build project, the customer may have only part samples, a CAD model or a 3D-printed model of the part they want to mold. While this may be advantageous to better visualize the product, it is absolutely necessary to have a complete detailed drawing of the product to minimize risk for all parties involved in the final decision.
A complete plastic part drawing should contain the following information at a minimum:
A 3D solid model of the part or a completely dimensioned 2D plan and section view;
Any small or intricate details blown up into additional sections or views, for example, ribs or bosses;
1）A detail showing any fits to other components; 2）Engraving, artwork and cavity numbering; 3）Mold label information (if in-mold labeled); 4）Surface finishes; 5) Any stacking details (if appropriate); 6) Part weight (using an assumed plastic density); 7) Part volume (if filled and weighed); 8) Center of gravity (if appropriate); 9) Identification of plastic or steel sizing;
Identify all split lines and parting lines, including any intentional mismatches. Once the part drawing is completed, it must be reviewed with the customer and internally at the moldmaker’s facility.
Review Checklist for Plastic Part Design
The following checklist can be used as a part drawing critique during the part design review meetings. Embedding a part design critique meeting into your mold design process can save thousands of dollars and weeks of mold build time.
Answering the questions below will ensure that a proper review of the part takes place and that all critical aspects of the part design have been considered and approved by the customer, and are acceptable to the moldmaker.
1) Is the drawing a plastic part drawing or “steel part drawing?” Is this clearly marked on the part drawing? A steel part drawing is the plastic part with shrinkage dimensions applied, so that the mold designer does not need to add shrinkage
2) This is often used when the shrinkages are not uniform around the part
3) Is the shrinkage defined? Is there one (1) general shrinkage or multiple shrinkages?
4) Are part weight and tolerances clearly shown?
5）Is all geometry defined (radii, angles and so on)? Are complicated details called out in blowups and section views such that the part design is fully understood?
6）Are all negative drafts on the part eliminated? Are all drafts defined, including ribs, bosses and sidewalls?
7）Are there any sharp corners on the drawing? If possible, a minimum radius of 0.25 millimeter (0.010 inch) should be used on plastic parts. A radius of 0.8 millimeter (0.030 inch) is the minimum recommended radii as the stress concentration is mostly eliminated above this.
8）Are the parting lines and all split lines defined? Are all intentional mismatches between core and cavity shown and defined?
9）Has a CAE flow analysis been conducted? Will the part fill and avoid any problematic weld lines and potential voids? Review the L/t ratio (length of flow/thickness) and confirm it is acceptable.
10）Are all venting locations shown and vent sizes defined?
11）Are all potential pinch points to the flow of the molten plastic eliminated? For example, are all thick sections that may cause “race tracking” of molten plastic eliminated?
12）Are horizontal sections (bottom/stack shoulder) 0.05 millimeters thicker to account for stack compression and ease of filling?
13) Are locations where sinks may occur (like at the end of a rib) called out? Are thick-to-thin transitions designed correctly to reduce sinks?
14) Is the gate position defined and an acceptable gate vestige called out? Usually, the acceptable vestige for a valve gate is flush with the molding surface or slightly into the molding surface to prevent interference. Normally acceptable vestiges are around 50–75% of the gate diameter if the gate is a hot tip. Is a dimple needed to hide the gate vestige?
15) Is allowable warpage called out?
16) Do the parts need to stack and de-nest? If so, is the stacking height shown, and is there a diagram showing the stacking of the parts?
17) Are all ribs and bosses shown in plan view, top view and side view?
18) For multi-cavity molds, is the cavity numbering identified?
19) Are all molding surface finishes defined?
20) Is all required engraving shown on the part? For example, does the engraving need to be mirrored on the molding surface?
21) Is any geometry to be left off until after the first test (pull rings, engraving)?
22) For critical dimensions, will the dimension be left “steel-safe” for the first run so that the sizing can be adjusted?
23) Have any deviations to standard tolerancing of molding surfaces and fits been noted?
24）Has the part drawing been reviewed with the customer and signed off?
Time for Approval
Once the part design has been critiqued and revised accordingly, the customer must approve it. This step is critical and must never be skipped. Ideally, part approval should take place before a detailed mold design begins so that the mold designer can note any changes in the design and account for the corresponding change costs. However, in today’s fast-paced environment, the mold designer must sometimes work parallel with the customer by completing some of the mold design concept while the part is still being finalized. This approved part drawing, along with the details of the mold design (typically called the mold design order or order confirmation), can now be used to complete the mold design.
Spending the time to critique and carefully evaluate the part before creating a mold design is always a good use of time. If a problem is caught and corrected during the part design review, it can save up to 100 times the cost to resolve the problem at the end of the project. A thorough plastic part design review represents just a small fraction of the time required to design and manufacture the mold, and it ensures that you and your customer have an agreed plastic part for the mold build project.
Plastic design typically specialize in a particular manufacturing area, such as injection molding or vacuum forming. This limitation precludes them from providing you with the optimum manufacturing process for your application. All products are ideally matched for injection molding due to part size, production quantities, or materials. An experienced plastic design will analyze your unique requirements and direct you to the optimum process. This objectivity benefits you with the most cost-effective plastic molding option to amortize your investment.
professjional plastic designer always designs every product to comply with manufacturing practices that match your vendor’s capabilities. These practices include details that are based on mold design, tolerances, material specifications, color matching, and part quality. Every design is modified to comply with your specific molder’s capabilities.
Industrial designers are continually challenged with preserving their concept design intent as it is transformed into a production design. This delicate process can be managed efficiently if the industrial design firm is knowledgeable about mold design and the specific plastic molding process. Integrated Design System has a comprehensive understanding of mold design and routinely translates its highly innovative designs into practical, easily molded plastic parts.
Plastic engineering expertise requires a broad knowledge of polymers, plastic molding, tool design, and requirements for the application.Integrated Design System is your choice when you want a guaranteed world-class design.
Injection molding is a complex process with countless variables despite its widespread use in different industries. Many factors can impact the final result, so you must start with an excellent design to help manage the manufacturing process and ensure quality output while minimizing resource consumption and production errors.
There are several positive ways that a good design can impact the injection molding process. In this article, we will explore some of the most crucial product design best practices for manufacturers.
Reduced Cost
The cost per part of the process can be significantly reduced with a good mold design. For example, designing a mold for longevity, reducing undercuts, material selection, and designing a family or multi-cavity mold can help reduce cost. In addition, a high-quality mold, designed accurately and with suitable materials, can last for a very long time while increasing production speed and further driving down costs.
Repeatability
The goal of injection molding is to manufacture many products with minimal variation between each piece within tight timeframes. Of course, many variables are intrinsic to the injection molding process, leading to discrepancies between each piece. Still, a well-designed mold can help increase the repeatability of the process. Plus, once a mold is designed and put in place, it lasts for a very long time, delivering significant return on investment (ROI) while fostering additional benefits like improved production speed and productivity.
Faster Output
The design, material choices, and other factors can increase the time and parts per cycle of the injection molding process. Reducing the length of each cycle means more parts per hour, allowing you to produce a large number of parts more quickly. Therefore, the more parts made per hour, the more productive the process.
Note that this can also affect the cost – higher productivity can drive prices down yet further, particularly when coupled with improved mold quality and reduced production errors.
Better Visual Result
A poor design can lead to many visual defects in the final part. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. A good injection mold design will take all of these factors into consideration, ensuring that the final product looks great.
Visual appearance is more than “mere aesthetics” – your customers will undoubtedly notice, mainly if their customers complain. Lines and marks mar the surface, leading to an inferior appearance despite using high-quality materials.
Durability
It’s essential to consider the durability of both the mold and the parts. The material and design of the mold itself can affect the number of parts that can be successfully manufactured from the mold before a replacement mold is required. The design of the mold can also impact the durability of the produced parts, reducing breakage. Less breakage and more outstanding part durability mean reduced production costs but also less tangible benefits, such as brand recognition.