Tools and molds are the backbone of the manufacturing industry. Cutting the tools for a production run can be among the most expensive costs associated with production. Even before mass production and prior to the advent of rapid prototyping technologies such as 3D printing, building a functional prototype was costly and time-consuming, putting it out of reach for many entrepreneurs and small to medium enterprises.
However, rapid tooling is quickly becoming a cost-effective and lean option for prototyping, and short-run or low-volume production. To learn more about how rapid tooling can save manufacturers money, engineering.com recently spoke with Raymond Cheng, founder of WayKen, a rapid prototype manufacturing service based in the manufacturing super-mecca, Shenzhen, China.
“With today’s product lifecycles shortening, product developers must move from design to manufacturing to lean production oriented short-run or low-volume production solutions. Rapid tooling is an extremely effective way to achieve results,” advised Cheng.
Depending on the process, conventional production tooling is typically made of high-durability tool steel. The familiar O1, D2 and P20 alloy grades were wear resistant and hardenable, but roughing, milling, grinding (and sometimes polishing)—all precision machine tool tasks—were costly and difficult. Modern ally steels and CNC machine tools helped, but the high cost and customized nature of tooling meant that parts needed significant production volumes to amortize tooling costs. The other alternative, soft tooling or partmaking on a custom basis, was costlier still on a per-part basis. Most production processes need tooling, and even if the cost can be controlled, time is a factor.
This process may take up to several months depending on the required parameters of the tool. The strategy behind rapid tooling is to make a less-durable tool which is engineered for a much shorter life than a conventional tool. This allows toolmakers to work with less expensive materials and faster manufacturing processes, reducing waste and saving cost.
“Compared with production tooling, rapid tooling is often a simper process that can provide fast and cost-effective production solutions for every aspect of manufacturability, such as mold design, mold materials and mold processing,” explained Cheng. “According to the needs of customers, this technique can usually help them reduce production costs by 50 percent or more.”
Wayken offers rapid injection molding Design for Manufacturability (DFM) services that cover every aspect of the injection molding process from part design, mold tooling design and materials selection to processing, declares Cheng.
“With 20 years of practical experience in traditional mold making and rapid tooling, our engineers will integrate a comprehensive interactive quote and manufacturability analysis and will be able to conduct design reviews to recommend the best technology for your custom prototype part. For example, gate type and location, parting line, draft, runner system, slide and insert, ejection, critical dimensions, tolerances and surface finishes—all matter when it comes time for production.”
Rapid tooling is a faster, more flexible and more cost-effective production solution designed for low-volume production of parts and prototypes. Like production tooling, rapid tooling involves different processing technology and equipment depending on the part design parameters. Rapid tooling can be made for a variety of manufacturing processes, including:
The term ‘rapid’ may bring to mind 3D printing, which is sometimes called rapid prototyping. 3D printing is a natural fit for fast turnaround of prototypes or small-batch parts, because virtually any CAD model can be printed in less than a day using a wide range of commodity or engineering materials, including metals.
According to WayKen, the most widely used printers for rapid tooling use direct metal deposition (DMD) or powder bed fusion processes. Additive manufacturing requires no fixtures or blanks—only universal powder or filament materials. However, the surface finish of printed parts is similar to that of cast parts, and will often require post-processing.
Computer Numerical Control (CNC) machining includes milling, drilling and tapping, turning, grinding and more. CNC milling is the principal process used for making production tooling, and it’s used for rapid tooling, too. Typical tolerance accuracy ranges from +/-0.005″ (+/-0.125mm) to +/-0.001″ (0.025mm) for CNC milled aluminum.
WayKen uses 5-axis milling machines because these machines can quickly locate blanks without complicated fixturing and can cut complex toolpaths that aren’t practical on ordinary 3-axis equipment. Whereas 3-axis machines can move the tool in x, y and z directions, 5-axis machines have two additional axes of rotation. This enables machining of complex features not possible with a 3-axis machine.
Aluminum is often the most effective material for rapid tooling, thanks to the low cost and machinability. Aluminum can be used for injection molds, dies, and even die casting molds. Aluminum tooling has a shorter life compared to steel tooling but is excellent for short to medium length production runs and has very good heat transfer qualities, a useful feature for injection molds.
CNC aluminum does have limitations compared to some more specialized processes. For example, because the material is cut by a spinning tool, internal corners must have a radius. Deep blind holes, oblique holes, or undercut features are not feasible. In addition, features on both sides of a part will require multiple machining operations to flip the part over and machine the other side.
In addition to metals, some plastic materials can also be machined. Plastics behave differently than metals in machining processes, so different cutting tools and feeds and speeds are needed to achieve high-precision tolerances and finishes. CNC machining can be an option for prototypes which are intended for molding or other processes in final production. Wayken also offers CNC prototyping services.
Electric discharge machining is a subtractive CNC process which operates by the same phenomenon which occurs when electrical arcing in a switch gradually erodes metal contacts over time. When an electrical arc occurs, the energy ablates and vaporizes a small area of the surface of the metal. EDM machines scale this phenomenon up, using a custom-shaped ‘sinker’ electrode or a wire to focus this ablation on a prescribed area of the workpiece.
Using this process, unique features such as rectangular holes, oblique holes or small features can be created. The process is also ideal for very hard materials such as Inconel or titanium, which are costly to machine with cutting tools.
These sinker electrodes are essentially reverse-cavity molds, and are typically made of soft, conductive materials such as copper or graphite. Rapid tooling can be an effective way to quickly prepare an EDM tool and begin work on a new order faster.
Urethane vacuum casting can be an excellent method of producing short-run or prototype parts which would otherwise be made via injection molding. This is a fast and inexpensive alternative for prototyping, pre-marketing or small batch production.
To use urethane casting, a master model of the part must be made. This model can be made using a wide range of rigid materials, including wood. The master model is suspended in a tank and silicone is poured around it. When the silicone hardens, it is cut in half and the master model is removed, leaving a mold cavity. These soft silicone molds typically last 10-15 castings, with the castings made using polyurethane resins.
When more than 30 castings are required, the master model can be used to make multiple silicone molds so that parts can be cast in parallel, saving time.
Above, we’ve overviewed some of the main processes for making rapid tooling. So, what industries benefit from these techniques?
The automotive prototyping process is long and expensive, but better use of faster, less wasteful rapid tooling could reduce the time and cost associated with building prototype parts and speeds time to market.
Because aerospace manufacturing typically deals with low batch volumes, it’s an ideal fit for tooling designed to produce a smaller quantity of parts. Because of the high cost, expensive materials, and complex design requirements of aerospace components, additive manufacturing processes are also a natural fit.
For obvious reasons, medical devices are subject to intense regulatory compliance. By speeding the production of functional prototypes, medical device manufacturers can successfully complete clinical trials and bring their product to market faster through medical device prototyping stage.
Post time: Jul-16-2019