"A Solid Solution for Moldmakers"
by Mike Morse, Technical Consultant at EDS (formerly SDRC)

Problem: "Good, Fast, Cheap--Pick Any Two."

Today's plastic injection moldmakers are faced with three apparently mutually exclusive requirements:
> produce molds of higher quality
> produce them faster than ever before
> produce them within tightening budget constraints

Most of the time moldmakers can succeed at two, while sacrificing the third. For example, to produce the mold faster and within budget, they may have to sacrifice quality. If they deliver a quality mold on time, they may not be able to make a profit. As global competition increases, meeting all three of these requirements will become even more critical to a moldmakers's success.

Quality
A quality mold must be able to meet the customer's tolerance requirements, typically within the range of 0.005" to 0.001". A quality mold must also produce consistently with no, or very few, rejects and must have low maintenance requirements. The mold must be durable enough to meet the production run; it must be efficient in filling and cooling the cavities; and it must be able to be repaired or retooled quickly. High-quality tools require fewer tryouts, need less hand work, and with the assistance of modern technology, can be produced in shorter times by less skilled workers.

Speed
Around the world, moldmakers are in a increasingly competitive environment in which delivery times tend to be the most critical requirement. Moldmakers are being forced to reduce delivery times and are being held responsible if committed dates are missed. Remaining competitive in the market requires continual reductions in delivery time. These increased time pressures make the process of simultaneously building multiple molds much more difficult. Coordinating manufactured components, subassemblies, and purchased components into the final mold assembly becomes much more difficult as the number of molds in process on the shop floor increases.

Cost
Aside from the inherent difficulties moldmakers encounter attempting to produce quality molds in shorter times, moldmakers also face the pressure of increasing overhead costs, increasing costs for raw materials, and declining costs of the molds themselves, all leading to an overall reduction of profit margins.

Compounding the Problem

Typically, moldmakers produce molds for prototype parts or production parts. While delivery time, quality, and cost are all very important considerations for all types of molds, the critical factor for prototype parts is usually the time to create the mold; and for production parts, the quality of the mold is the most important. However, many moldmakers produce both types of parts and must confront all three criteria. And, in the midst of these time, quality, and price concerns, there are still other factors that compound the problem even further.

Complex Parts
First of all, the molds themselves, and the parts that they produce, are becoming more complex. Part designs are incorporating more complex details, often combining features into one part that formerly required several parts from multiple molds. Mold design resources are continuing to becomes more capable in modeling and simulating even the most complicated components and mechanisms, allowing more complexity to be incorporated into the mold design.

Next, moldmakers are continuously attempting to reduce or eliminate post-molding processes. Steps in product assembly and finishing can be eliminated or reduced by incorporating more detail in the mold itself. Additionally, as parts become larger, the molding process itself can become more complex. One example: parts that are more complex require concise valve gate sequencing to assure equal pressure throughout the mold.

Finally, more moldmakers are also getting involved with the actual product design itself, collaborating with the customer to insure that from the very early stages, the part design meets the requirements of the molding process. This early collaboration adds complexity to an already difficult task. Collaboration does allow the moldmaker to give input during the product design, helping to insure that the part is moldable. It may also give the moldmaker more lead time to order and prepare the mold base, and perhaps even enough time to begin machining in advance of the finalized part design. However, this collaboration also makes more work for the moldmaker, requiring more skilled personnel, and may draw valuable resources away from the basic mold design tasks.

Core and Cavity Design
One of the most common and time-consuming design functions of any moldmaker is that of core and cavity design. See Figure 1. At a minimum, core and cavity design means the creation of the mold parting surfaces, inserts, lifts and slides.

When a moldmaker receives the initial product design, it must be analyzed to determine the amount of work required to create a functional mold that can produce the part. The moldmaker must determine and account for things like:
> part shrinkage
> undercuts
> location and appearance of shut offs and of parting surfaces
> sufficient draft angle
> minimum fillet radii
> overall moldability of the part

The amount of time required to design and model these mold-specific features accounts for a large percentage of the overall moldmaking effort.

Once the cores and cavities are designed, most moldmakers also design the mold base itself, defining the mold base size and style, and designing, analyzing, and locating gates, vents, runners, cooling lines, ejector pins, and actuators, etc. This can be a very time consuming effort.

Numerical Control
Another aspect of core and cavity design is preparing the part for NC programming and creating the required NC toolpaths. Electrodes must also be designed. Rough, semi, and finish toolpaths must be generated for the direct milling of the cores and cavities, and for any electrodes. In some cases, wire EDM toolpaths may also be required. The amount of time spent generating NC toolpaths can be significant. Poorly designed geometry or difficult machining conditions can quickly add complexity, and may require manual intervention into an otherwise semi-automated task.

Most moldmakers don't just design the mold; they are also required to produce the mold itself. On the production side, a majority of time is spent in 3-axis milling of cores and cavities. This means rough machining of the cores and cavities, performing any required secondary machining, and then finishing to the required tolerances. Mold base plates themselves also require some machining: to add runners, cooling lines, and pockets for inserts, and to create holes for ejector pins and core pins.

Process Progression

Over time, CAD/CAM software tools have progressed from 2D to 3D surfacing to 3D solids. While each technology has reduced the manual effort required by the moldmakers, each technology plateau had its drawbacks in addition to its benefits.

2D CAD Software
Initially, mold design was performed with 2D CAD software, such as that provided by AutoDesk or Cadkey. These early CAD systems were little more than 2D electronic drafting programs. Creating mold parting surfaces with 2D software was difficult for all but the simplest of cases, often requiring many cross-section views.

Although mold bases could be well documented with 2D views, keeping track of all the components became more difficult as the mold became more complex. Moreover, a 2D CAD representation of complex surfaces provided almost no value to the machinist tasked with milling them.

3D Surface Modeling
After the introduction of 3D surface modeling software, utilizing b-splines and NURBS surfaces, complex parting surfaces could be visualized and designed in their true form. Furthermore, 3D designs could be transferred directly to the CAM software, facilitating toolpath creation. In fact, before 3D surface models were available, automated NC toolpath creation existed only for simple wireframe shapes. See Figure 2.

Although 3D surfacing technology made the creation of shut-off surfaces and parting surfaces easier, the task could still involve more design work than that of the actual product model. For example, part designs need to be analyzed to determine appropriate draft angles and, if missing, draft must be added by the moldmaker. Adding or changing draft angles on a complicated surface model can be tricky, often requiring an experienced CAD designer.

Complex parts, or even simple parts with non-flat parting lines, have to be analyzed to calculate and locate split lines, and to generate parting surfaces. Even with sophisticated 3D surfacing tools, parting surfaces, may need to be created manually, often requiring difficult blends. Parting surface creation becomes even more complex when there are undercuts, requiring slides or collapsing cores. And, of course, the whole core/cavity design process needs to be repeated from scratch if the part design changes.

3D surfacing tools did little to help the mold base designer, however, since mold bases are not made from sculptured surfaces, but from plates, pins, and screws. In fact, for moldbase design, these 3 D CAD systems could be slower and more difficult to use than the old drafting systems.

And Finally--3D Solids
3D solid modeling is the most recent development in CAD technology. Solid modelers can create true geometric volumes, and have the ability to create complex shapes similar to those of surface modelers. In fact, some solid modelers have integrated surfacing tools within them, and can provide the same levels of geometric complexity as traditional surface models.

For the moldmaker, 3D solid volumes are extremely beneficial in the creation of cores and cavities. In one modeling technique, the volume of the modeled part can be extracted, or "cut", from the volume of the mold base insert, providing a simple and acceptable solution if the parting line is planar.

In another option, more appropriate for complex (non-planar) parting surfaces, the part design, coupled with the parting surfaces themselves, can be used to "partition", or divide, the volume of the mold insert, automatically yielding both a core and cavity in one step.

Advances in solid modeling software have provided the moldmaker with even more automated tools. Because the solid volume is fully closed, and has the understanding of an "inside" and "outside", a great deal of information can be garnered automatically. Designs can be checked for proper draft angles, with undercuts and vertical surfaces highlighted for correction. On complex shapes, the parting line curves themselves can be created easily by employing a "silhouette" function. Openings requiring shut-offs can be identified and closed with a membrane surface.

In addition, specialized software exists to automatically create the parting surfaces as well, including those where slides may be required. User interaction with those tools provides for a fast and simple method of visualizing, modifying, and verifying even the most complex parting surfaces.

History, Analysis and Documentation
Solid modelers often keep track of the steps used in the development of a part of a mold. By having this part history available, the designer can go back to previous operations and change them, without loosing the effort of modeling subsequent steps. Parts with a history enable the changing and testing of various parameters and the creation of derivative parts. This history feature also vastly improves the ability of other designers to understand the part and its creation method. This is especially important to those who may not have been involved with the original part construction, but who may be tasked with making corrections or revisions.

Solid models also lend themselves directly to structural by CAE applications. Just as the part designer can test the part for structural integrity and durability, the mold designer can test the mold for plastic fill simulation, mold cooling, and part warp. See Figure 3.

As the acceptance of 3D models increases, the reliance upon 2D drawings decreases. Prints on paper or mylar are no longer on the critical path to production. While 2D documents are still a requirement in many industries, they are seen as secondary in importance, The 3D model is now considered the "real" or "master" design. Even though fully detailed drawings are off the critical path, solid models actually lend themselves to documentation. Dimensions and annotation may be added directly to the 3D design, which may then be transferred to a VRML format, appropriate for viewing over the Internet, or even internally on the shop floor.

Alternatively, 2D views of the model can be assigned, and dimensions can be created, positioned, and plotted, all with associativity back to the original design. Cross-section cuts can be developed automatically. Bills of material, based upon the model components, can be generated directly from the assembly, and automatically placed on the drawing.

Mold Base Layout
Solid models can also assist in the creation and analysis of the mold bases themselves. See Figure 4. The mold base represents the business end of the injection molding machine. Each one is customized to the product being produced. The design of the mold base determines how the plastic will be injected into the cavity, how the material will be cooled, and how the result will be ejected from the cavity. Mold bases are typically composed of many standard parts and subassemblies. With 3D solid modelers, mold plates, pins, sprues, and other components can be generated automatically from a manufacturer's part catalogs. Standardized mold base components from companies like DME, HASCO or FUTABA can be stored and retrieved quickly with their sizes adjusted through a small set of user parameters.

In a parameterized, dimensioned and constrained mold base design environment, the positions of pins and the required holes in their associated plates, for example, can be maintained even when dimensions change. This kind of "smart part" technology speeds the development of the mold base design and greatly simplifies making changes.

Solid modelers can handle the multiple parts of a mold base as a single assembly, greatly improving visualization. Solid models can be viewed as a wireframe only, in a "hidden line" mode, or as fully shaded solid representations. Some systems even provide photo-realistic rendering, with highlights, shadows and textures. This enhanced visualization greatly assists moldmakers, especially with complex designs.

Mold base assemblies themselves can be stored, modified, configured, and reused in a solid modeling environment. Moldmakers can now build mold base assemblies as quickly as the old 2D layouts were created. Since individual assembly components and subassemblies can be held together by constraints, both geometric and dimensional, design changes can be quickly accommodated.

With solid modelers, the volume of the part can be associated to the volumes of the core and cavity, allowing for an automatic update if the part design is modified. This ability to accommodate part design changes means a great reduction in time spent remodeling and redesigning the mold base. This associativity may propagate to the toolpath as well.

Because solid modelers can deal with even the simplest plates and pins as true volumes, interference can easily be detected. When all the components within the mold are modeled as solids, mechanisms within the mold base, like slides or ejectors, can be tested for motion, stresses and collisions.

Additional Benefits from Solids
Solid models can also enhance NC toolpath creation. Solid designs may incorporate common features like holes, slots, or bosses, which can be machined automatically by predetermined tools and methods. Gouge avoidance against the part, the machine tool, and any clamps or vises, is facilitated by knowledge of solid volumes. Associativity of the toolpath back to the model may mean automatic updates are available if the design changes.

Some solid modelers also include data management software, making it possible for multiple designers to work on the same part or assembly at the same time. This can mean true concurrent engineering between the part designer, the moldmaker, and the NC programmer. Sharing work in this fashion means mold designers can begin their work sooner, handle changes easier and more quickly, spread the work among several people to get faster results, and improve throughput by eliminating wasted time spent on serial processes.

In these database management environments, a designer can be automatically notified when a part changes, allowing immediate access to the latest versions of a design, assembly, and drawings. This also eliminates the problem of different people working on different versions of the same part.

Next Step--Integration

Moldmakers are looking for an integrated suite of software tools that solves the needs of design, analysis, and toolpath creation. Furthermore, moldmakers are looking for software that can manage non-geometric data, like part revisions, bills of materials, engineering change orders, tool libraries, and part catalogs. Not only are moldmakers moving toward integrating their internal CAD, CAM and CAE systems, they are also working to integrate their processes with those of their customers and their suppliers.

Some software systems, while claiming to individually perform "best-in-class" CAD, CAM, and CAE tasks, often do not work well together. Initially, part designs were transferred to the moldmaker via 2D drawings. Today, however, moldmakers cannot afford the time required to completely remodel a part from a drawing, just to get the part into their CAD/CAM system so they can begin the mold design process.

Now, with the almost universal acceptance of 3D CAD for part designs, data is more commonly transferred to the moldmaker by means of IGES files, either on magnetic tapes or through the Internet. Unfortunately, with this process, valuable time can be lost transferring data, fixing errors, and duplicating efforts. Furthermore, with different non-integrated systems, it is possible that multiple, non-identical versions of the same part may exist, creating confusion, errors and loss of time.

Integrating CAD/CAM/CAE systems, however, eliminate data translation, and often provide additional benefits, like associativity between the part, the mold design, and the resultant toolpaths. This is a huge advantage.

Enabling Collaboration
As the scope of the moldmaking task widens to include more up-front product design, and as moldmakers become more integrated with their customers and suppliers via the Internet, they are also looking for collaboration tools that enable communication, allow visualization, and automate documentation, regardless of specific CAD/CAM systems or of physical locations.

Just as data management tools allow for designers and NC programmers to work in a concurrent engineering environment, the Internet, and 3D viewer technology, enhances communication and understanding. It is no longer necessary to translate a large and troublesome IGES file just to see what a part looks like. Instead, using standard software, images can be viewed interactively, in 3D, without the need for high-powered computer hardware.

Web-based data sharing allows for moldmakers, product designers and suppliers to collaborate and cooperate in ways never before possible, thus eliminating redundancy, and minimizing errors and confusion, all while improving quality and shortening planning and production times.

Electronic business-to-business (B2B) communications are becoming increasingly important. Moldmakers use the Internet to send and receive e-mail, to transfer geometry data and NC toolpath files, and to view photos or other representations of the product. Quotes can be provided on-line, material can be ordered, software and utilities can be downloaded, and information can be gathered from a variety of web sites.

Therefore, the ultimate technology for moldmakers is one that not only enhances and integrates the design, analysis and NC toolpath creation tasks, but also integrates information and processes, both internally and externally, via the Internet.

Conclusion: "Good, Fast, Cheap--Pick All Three."

While moldmakers face these constant pressures to reduce delivery times, cut costs, and improve quality of their products, they no longer have to rely on using the traditional, labor intensive, mold design techniques. They can now move away from 2D prints and wireframe models, and instead embrace 3D surfacing and solid modeling tools.

Specialized software is available for moldmakers to automate the task of analyzing part design, and creating parting surfaces. Moldmakers can leverage the solid design directly for CAE applications, like mold filling and cooling. Mold base assemblies can be created to take advantage of industry standard components with intelligence and associativity to the original part. Mechanisms can be simulated and interference can be detected automatically insuring correct mold operation.

Advances in machining and machine tool technology, like high-speed machining and multi-axis milling, are shortening production times and improving quality. Specialized CAM software, developed to handle these new machining styles, further reduces the effort required to program and verify these toolpaths.

These advances in technology, both in software and in hardware, are giving moldmakers the ability to have it all. With the correct technology, moldmakers can produce higher quality molds, they can deliver their molds on time, and most importantly, they can still make a profit.