Design for Manufacturing (DFM)
in Plastic Injection Molding
In the world of plastics, Design for Manufacturing (DFM) is the combination of art, science
To achieve its objectives, DFM requires collaboration between the molder, OEM and customer. It must capitalize upon best in class manufacturing processes. Its principles drive a scientific molding process that includes materials selection. It needs to acknowledge and work within and up to the maximum performance capabilities of the molder’s manufacturing equipment. It must utilize state of the art technology like simulation and enterprise resource planning software in the design process, and robotics and process control systems for manufacturing.
On this page, Rosti explores DFM to help our customers and prospects understand its role during the design validation process, prior to tooling kick off. You can download this entire page as a PDF here, read through the entirety of our insights and observations by scrolling down this
Design for Manufacturing (DFM) involves designing a product that optimizes manufacturing efficiencies for the equipment and/or process used in its production in order to realize the lowest possible unit costs at the highest possible quality. The most important reason for integrating DFM into manufacturing a plastic injection molded product is that 70% of its manufacturing costs can be determined by design decisions.
DFM requires choosing the right manufacturing process for a part or product; investments in different technologies, using state of the art design principles (discussed below
DFM is an instrumental part of another customer demand: lowering manufacturing and assembly costs. A simple look at the way this is accomplished is presented below; however, when a DFM plan is completed deskside, it should be an engineering document laser-focused on getting a “just right” balance of quality and costs.
Learn more about how DFM works into the comprehensive injection molding process in our guide: Injection Molding 101.
Source: Computer-Aided Manufacturing, Second Edition, Tien-Chien Chang, Richard A Wysk, and Hsu-Pin Wang. Pages 596 to 598. Prentice Hall 1998
Source: Design for Manufacturing and Assemble, D. Havel, https://www.slideshare.net/dhaval6693/dfma-57014998
Beyond just estimating manufacturing costs, your injection molder should be using DFM principles to reduce the costs of components, reduce the costs of assembly, reduce the costs of supporting production, and to identify the impact of DFM decisions on other factors throughout the entire design and production process.
Another reason for selecting a
Before a mold is created, best DFM practices for plastic injection molded parts incorporate the following critical elements:
Considering Material Shrink Rate:
Shrinkage is the contraction of the molded part as it cools after injection. All materials have different shrink rates depending on resin family (amorphous vs. crystalline materials), mold design, and processing conditions.
Draft:
How features of a part are formed in a mold determines the type of draft needed. Features formed by blind holes or pockets (such as most bosses, ribs, and posts) should taper thinner as they extend into the mold. Surfaces formed by slides may not need
Uniform Wall Thickness:
Uniform wall thickness throughout
If sections of different thickness are required, make the transition as smooth as possible allowing the material to flow more evenly inside the cavity. This ensures the whole mold will be fully filled and will ultimately decrease the chance for defects. Rounding or tapering thickness transitions will minimize molded-in stresses and stress concentration associated with abrupt changes in thickness.
Incorporating the proper wall thickness for your part can have drastic effects on the cost and production speed of manufacturing. The minimum wall thickness that can be used depends on the size and geometry of the part, structural requirements, and flow behavior of the resin. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0.080" – 0.160"). Thin wall injection molding can produce walls as thin as 0.5mm (0.020"). Work with an experienced injection molder and design engineer to be sure the proper wall thicknesses are executed for your part’s design and material selection.
Radii to Edges:
In addition to main areas of a part,
Ribs:
Many designers think that by making the walls of a part thicker, the strength of the part will increase. When in reality, making walls too thick can result in warpage, sinking, and other defects. The advantage of using ribs is that they increase the strength of a part without increasing the thickness of its walls. With less material required, ribs can be a cost-effective solution for added strength. For increased stiffness, increase the number of ribs rather than increasing height and space a minimum of two times the nominal wall thickness apart from one another.
Draft Angle:
How features of a part are formed in a mold determines the type of draft needed. Features formed by blind holes or pockets (such as most bosses, ribs, and posts) should taper thinner as they extend into the mold. Surfaces formed by slides may not need
Finishing:
Surface finish options for plastic injection molded parts vary depending on part design and the chemical make-up of the material used. Finishing options should be discussed early in the design process as the material chosen may have a significant impact on the type of finish implemented. In the case where a gloss finish is used, material selection may be especially important. When considering additive compounds to achieve
Consideration of these elements is fundamental for integrating engineering and manufacturing expertise to catch mistakes, see opportunities for efficiencies and cost reduction, and even assess the viability of contract requirements. Typically, your injection molder will conduct a detailed analysis of these elements with your team well before the tooling process is initiated.
DFM is not a “
Design for Manufacturing |
Design for Manufacturing (DFM) describes the process of designing or engineering a product to reduce its manufacturing costs, allowing potential problems to be fixed in the design phase which is the least expensive place to address them. Depending on various types of manufacturing processes there are set guidelines for DFM practices that precisely define various tolerances, rules and common manufacturing checks related to DFM. |
Design for Functionality | Throughout the plastic part design process, it is imperative to keep |
Design for Assembly |
Design for assembly (DFA) is a process by which products are designed with ease of assembly in mind with the ultimate goal of reducing assembly time and costs. The reduction of the number of parts in an assembly s usually where the major cost benefits of DFA occurs. |
Design for Sustainability |
Design for sustainability focuses on designing parts with print measurement intent in mind - sustaining tolerances with proper measurement on an ongoing basis. |
Material selection is a critical part of the DFM path to high quality/low cost/fast production plastic injection molded parts and products. The sheer number of types of plastics and their associated properties makes discussions between material providers, injection molders and product manufacturers critically important, as addressing specific needs early in the design process is key to avoiding costly changes later.
Materials selection affects strength and flexibility, temperature resistance, durability, appearance, toughness, life-span, and (of course) production cost. Other needs can include:
When it comes to selecting the right material, it takes experience, expertise
Interested in downloading this guide as a PDF? Click Here.
Chemical resistance | Child safety |
Color | Compliance with FDA standards |
Compliance with NSF standards | Compliance with REACH standards |
Compliance with RoHS standards | Dielectric properties |
Economic or cost constraints | Embossing requirements |
Environmental conditions | Finish requirements |
Flexibility | Food safety |
Heat, flame or burn resistance | Material strength |
Mechanical conditions | Need for reflectivity or transparency |
Pressure resistance | Rigidity |
Shelf life | Weight resistance |
Manufacturers use a wide variety of plastics to mold parts incorporated into products and have increasingly begun to replace other materials like bronze, stainless steel, aluminum, and ceramics. Some of the most popular reasons for using or switching to plastic include longer overall lifespan of the part, reduced wear on other components of a product, faster production line speeds, corrosion resistance
Source: Grandview Research, Injection Molded Plastic Market Report by Raw Material, https://www.grandviewresearch.com/industry-analysis/injection-molded-plastics-market
Aligning with your injection molding partner to choose the best resin early in the design for manufacturability process, is crucial to a part’s production success.
Material selection plays a critical role in the strength and flexibility of your molded part. Addressing specific needs early in the design process can help you avoid costly changes later. Balancing characteristics like stiffness, durability, toughness, and others are key in achieving optimal part functionality. Additionally, it’s important to understand the key differences in some of the more commonly used resins.
ABS (acrylonitrile butadiene styrene) is a common injection molding material that can be sourced and molded relatively easily, at an accessible price point. It’s a strong, sturdy material that offers good impact resistance, is easily machined, and meets a variety of aesthetic requirements. The resin is not ideal for parts that will be subjected to sustained intense heat as it will warp or melt above / around 200 degrees Fahrenheit.
Polycarbonates are a high-grade class of thermoplastics that are easily molded and often increases shatter resistance. Naturally transparent, polycarbonate is ideal for high-strength glass-like applications (safety goggles, medical lab applications and more). Polycarbonate isn’t suited for applications where a higher degree of flexibility is needed or colored aesthetic choices.
Glass-filled nylon is a reinforced thermoplastic, where the base nylon resin has glass fibers added to it for extra strength and heat resistance. This resin is also more nonconductive to electricity than many others, but despite
Polypropylene is a flexible thermoplastic that is suitable for industrial and consumer applications. It’s known as being a highly pliable resin that can be manipulated in many ways without losing its original shape. Polypropylene also offers resistance to solvents, chemicals
Acetal is known to provide great friction resistance and is a highly rigid material. It can be easily colored and dyed in the molding process; however, does not offer superior heat resistance.
One of the most vital steps when preparing for injection molding resin selection is to create a comprehensive material selection list of requirements for the product. The list should most certainly include price target and resin availability – as resin availability can be a risk and backup resin choices should be considered.
It's also important to consider that some characteristics of high heat and exotic resins are unique and may perform differently from one application to another. To realize both the design and material’s fullest benefits, experienced design engineers and injection molders have a number of factors to consider.
Design for Manufacturing a plastic part or product, prior to building
In the design stage, the plastic injection molding partner, OEM
Like other components of the DFM approach, surface finishing is part of the cost/quality/customer satisfaction formula that must occur at the beginning of a contract.
Finish | SPI* Standard | Finishing Method | Typical Surface Roughness Ra (μm) |
Super high |
A-1 | Grade #3, 6000 Grit Diamond Buff | 0.012 to 0.025 |
High |
A-2 | Grade #6, 3000 Grit Diamond Buff | 0.025 to 0.05 |
Normal glossy finish | A-3 | Grade #15, 1200 Grit Diamond Buff | 0.05 to 0.10 |
Fine semi-glossy finish | B-1 | 600 Grit Paper | 0.05 to 0.10 |
Medium semi-glossy finish | B-2 | 400 Grit Paper | 0.10 to 0.15 |
Normal semi-glossy finish | B-3 | 320 Grit Paper | 0.28 to 0.32 |
Fine matte finish | C-1 | 600 Grit Stone | 0.35 to 0.40 |
Medium matte finish | C-2 | 400 Grit Stone | 0.45 to 0.55 |
Normal matte finish | C-3 | 320 Grit Stone | 0.63 to 0.70 |
Satin textured finish | D-1 | Dry Blast Glass Bead #11 | 0.80 to 1.00 |
Dull textured finish | D-2 | Dry Blast #240 Oxide | 1.00 to 2.80 |
Rough textured finish | D-3 | Dry Blast #24 Oxide | 3.20 to 18.0 |
As machined | - | Finished to the machinist's discretion | 3.20 (with visible machining marks) |
Source: K. Varotsis, “Injection Molding SPI Surface Finishes”, Hubs https://www.hubs.com/knowledge-base/injection-molding-spi-surface-finishes/#finishes
Other Plastic Part Finish Options Include:
In recent years, plastic injection molders have turned to the principles and technologies associated with scientific molding. The goal of scientific molding is to (1) save developmental costs and time by eliminating trial and error in the design process, (2) create dependable, defect-free tooling that eliminates costly mold rework, improves part quality, and accelerates time to market, and (3) create a repeatable and easily auditable manufacturing process.
The technology of scientific molding is delivered through simulation software like SOLIDWORKS® Plastics Premium software (mold flow simulation) and executed through robotics and process control systems like RJG eDart® that produces consistent,
Using and integrating technologies supporting the plastic injection molding DFM process is challenging. It involves communication and collaboration between molder, OEM and customer, across many different disciplines.
SOLIDWORKS® Plastics delivers easy-to-use simulation for analyzing plastic parts and injection molds. It simulates how melted plastic flows during the injection molding process to predict manufacturing-related defects so you can quickly evaluate part manufacturability while you design.
Plastics manufacturing is a highly competitive, global industry where businesses are presented with both time and cost challenges. Avoiding delays and reducing risks for costly design changes can mean that your product gets to market faster than your competitors.
The sharp line that was once drawn between development and production is now, oftentimes, blurred with manufacturers leaning on industry design experts to become involved in the design for manufacturability process. In fact, manufacturers rank design as the top factor in reducing their overall manufacturing costs.
Over the years, best practices for tooling and part manufacturing have changed substantially. While production checklists are still critical components of the process, the work that happens earlier in the development cycle is what creates real efficiencies in regard to time and budget. When a tool-maker / injection molder is involved early in the development cycle, customer objectives are understood and unexpected surprises are avoided.
Are you looking for an injection molding that can provide expert consultation from design to production completion? Connect with Rosti's knowledgeable team members that focus on all areas of design for manufacturability, development, and production.
Rosti is an advanced plastic manufacturer known for innovation and technology including plastic part design for manufacturability support, material selection, production, and much more
Our DFM and simulation capabilities, our ability to leverage robotics systems and automation, and our world-class ERP technology
We can manufacture products from simple to highly complex at cost, quality, and production rates that are second to none.
For a discussion of our approach to DFM and to discuss your next project, Contact Us today.
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