Designing a tool isn’t just about making a perfect product – it’s also about making the tool last as long as possible. Many buyers are focused solely on the production and quality of their product, but it's important to keep in mind that a tool must be in spec to make a product that is in spec. Even if you don't have a hand in designing or maintaining tools, it's important to understand the process and how each decision you make can affect your product's tool.
The most crucial part of the entire tooling process is designing the tool itself. It's important to get the design perfect before cutting the tool, because errors can be costly. Allow your contract manufacturer (CM) to work with a toolmaker to design the tool while you worry about the design and function of the product. Choosing a CM that offers Design for Manufacturing (DFM) services will prove most beneficial during this process (see more on DFM below).
The first element to nail down is the category of tooling required, which is driven by your anticipated production quantity. Determine the life expectancy of the product first, and then work backwards to determine tool requirements that will support the product's needs. Your tool will fall into one of three quantity-driven categories:
- Low-volume (prototype) – up to 5,000 or 10,000 parts*
- Medium-volume – up to 100,000 or 150,000 parts
- High-volume – up to 1 million parts
*Quantities will vary depending on part, material, fabrication, maintenance, etc.
After determining which of these categories your product best fits, the next decision will be whether to opt for a soft or hard tool. This is largely determined by two factors: production quantity and product material.
Soft tools are typically made of urethane. While they are less costly, they also have shorter lives and limited features (e.g., you may have to sacrifice porosity). Some examples of soft tool processes include sandcasting, thermoforming and soft injection molding. Using soft tools for small production runs (1,000 to 10,000 parts) can help keep your investment at a minimum and result in a shorter ramp-up time.
Unlike soft tools, hard tools are made of long-lasting materials like steel. High-density injection molding tools could produce up to 100,000 shots for metals or up to 500,000 shots for plastics, as long as the tool is well maintained. Hard tools should be used for larger production runs, parts with complex geometries and high-temperature materials. If your production run is smaller (and so is your budget), aluminum is a less expensive – but much less durable – alternative to steel.
Mold Flow Analysis (for Plastics)
Before finalizing a design, a toolmaker should perform simulations for pressures and flows to make sure the tool will perform as expected. Mold flow analysis software reveals potential functional and cosmetic defects in the final product, including weak spots and stresses. A toolmaker can also use this software to identify the best position for gates and ejection pins by analyzing flow and fill rates. Working with a CM who has these capabilities will result in a better designed and longer lasting tool.
Benefits of Design for Manufacturing (DFM)
Design for Manufacturing (DFM) is the method of design for ease of manufacturing of the assortment of parts that will form the product after assembly. Working with a CM that provides DFM services will ensure your part isn’t overdesigned and can actually be manufactured. Sorting out product design manufacturability at the start will play a significant role in efficient tool design.
A successful DFM approach requires open communication with your CM and a clear understanding of your product’s life expectancy, usage and appropriate materials. If you're thinking that you could bypass this DFM step and simply have a Chinese factory make your product, you're absolutely right. A factory will happily make your product. But without any design analysis or optimization, you may very well end up with a non-compliant, cosmetically disappointing product. Why take such a risk?
Choosing Tool Material
Tool material has a major impact on performance and life expectancy. A toolmaker will determine which material is best depending on the geometry, product raw material and number of shots required. The ultimate goal is to make a tool as hard and consistent as possible based on thermal conductivity requirements. For instance, very high quality materials can withstand the shrinkage and growth of thermal changes, whereas poor quality materials will crack. Investing in good quality tool material can potentially double the life of the tool.
When You Need a Stronger Material
- Multi-axis tools. These tools can be highly complicated, outfitted with multiple slides to pull pins out. When dealing with a multi-axis tool, the material needs to be extremely durable to endure the friction and erosion of these constant movements. For instance, a high-grade alloy tool steel might do the trick.
- Products made with abrasive materials. If the tool will be filled with abrasive raw materials (e.g., those with glass fibers or acetal) to enhance strength or rigidity, you need a strong tool material that will not erode quickly. One alternative is to add a soft metal wear plate to the tool wherever a core slides in and out. This way the plate will erode (rather than the tool itself) and can be replaced when necessary, ultimately extending the life of the tool.
Coatings can be applied to a tool to prolong its life (e.g., a nickel plating will harden the surface). While coatings can be advantageous, your best bet is always to start off with the right tool material rather than depending on coatings, which can crack and chip off over time. Warning: Using materials with drastically different thermal properties is a bad idea since they will shrink and expand at different rates, creating gaps in the tool.
PEG Design + Tool Fabrication
Chances are your contract manufacturer will send you a PEG (parting line/ejector placement/gate location) design for review before the tool is cut. You should carefully review the PEG to understand where these features are located and how the design will affect your final product, both aesthetically and functionally. Your CM should also ask for your approval on the PEG before the tool design is finalized and fabricated.
Once the design is completed, the toolmaker will begin fabrication. A third party is often enlisted to apply a heat treatment to harden the tool. A heat treatment certificate should be provided and verified. The tool is then shipped to the manufacturer's location.
Like any sophisticated piece of machinery, a tool needs to be properly maintained throughout its life to ensure it continues performing as expected. After design, preventive maintenance is the most important aspect of tool performance. A regular maintenance schedule should entail the following:
- Clean tool after a specified period of significant use (TBD by supplier)
- For plastics: Clean with fire, brushes, scraping tools
- For metals: Clean with scouring process followed by polishing or lapping
- Inspect tool to track degradation
- Inspect at minimum increment of 10-20% of tool life, or after each significant use
- A tool maintenance expert should conduct these inspections
- Report findings
- Detailed report should be written after each inspection and at end of tool's life
- Keep a log throughout the tool's life to determine weak spots
If you're concerned that tool maintenance is lacking, you can ask your CM if the supplier keeps a regular maintenance schedule or log book.
What Kills a Tool
Even if regular maintenance is performed, tools sometimes wear out earlier than anticipated. Below are two common reasons tools die young:
- Feature wear. The cavity core wears out due to high pressure and temperature. Metal will slowly erode the features out of the tool and and geometry will grow out of spec.
- Heat checking. The material's surface is heated and cooled so much that it cracks like mud all over. You can provide a temporary fix by polishing it, but the electrochemistry of the material actually changes, so eventually the tool must be re-fabricated.
- A tool must be in spec to make a product that is in spec
- Even if you aren't involved in the tool design, you should understand the process and how product design and subsequent changes can affect your tool
- Tool life expectancy depends largely on material and maintenance
- Investing in a good quality tool material can potentially double the life of the tool
- Supplier should have a preventive maintenance schedule for all tools