Automation of the Mold Development Process

Three dimensional-based mold design solutions are being used for the development of injection molds, allowing mold tooling companies to shorten their development times and automate mold manufacturing. Also with 3-D, the quality of the design gets better because of the excellent possibilities to analyze the design.

To support the user as much as possible, a high-end mold design system has to provide such features as a 3-D standard catalog, automatic creation of a bill of materials and CNC programs as well as the possibility to store the moldmaker's knowledge by integrating its own standards and design methods.

The growing complexity of today's plastic and die cast parts makes it necessary for the mold design system to provide both the ability to handle free-form surface data well and to manipulate this surface data - regardless of its originating source or system. Also, because a mold is a complex assembly with many predefined rules, the mold design system should know these rules and automatically set the corresponding constraints.

Based on the 3-D data of the product, the core and cavity have to be designed first. Modern CAD systems can support this with calculating a split line for a defined draft direction, splitting the part in the core and cavity side and generating the run-off or shut-off surfaces. Then, in the conceptual stage, the positions and the geometry of the functional mold components - such as slides, ejection system, etc. - are roughly defined. With this information, the size and thickness of the plates can be defined and the corresponding standard mold can be chosen from the standard catalog. If no standard mold fits these needs, the standard mold that comes nearest to the requirements is chosen and changed accordingly - by adjusting the constraints and parameters so that any number of plates with any size can be used in the mold. Detailing the functional components and adding the standard components complete the mold. This all happens in 3-D.

Through the use of 3-D and the intelligence of the mold design system, typical 2-D mistakes - such as a collision between cooling and components/cavities or the wrong position of a hole - can be eliminated at the beginning. At any stage a bill of materials and drawings can be created - allowing the material to be ordered on time and always having an actual document to discuss with the customer or a bid for a mold base manufacturer.

Simultaneous engineering is another key expression that has to be supported by a mold design system in two ways. When there is a tight timeline, the system must allow for more than one designer working on the same mold at the same time. Also, even with a part file or part database, which is in its early development or which is expected to be changed drastically, it must be possible to complete a preliminary mold design and then import the new database after it's finalized.

Molds Are Complex Assemblies

Even with small plastic injection parts, the number of components in a multi-cavity mold can easily reach several hundred and the number of part and assembly drawings can be numerous. The parts of a mold differ very much in shape and function. Besides the usual standard components such as screws, ejectors, bushings and plates, the assembly also may contain slides and inserts, which have part contours and therefore the same complex geometry as the corresponding area of the part.

For example, with this one plastic part, three slides and two inserts are necessary; there are now five components with part detail. If we determine the need to have a multi-cavity mold with six cavities, there are 30 components with part detail and probably some ejectors that also will need part detail at their top.

Within this same mold there are around 150 screws and 60 ejectors. A characteristic for a mold as a complex assembly is therefore not only the number of components, but also the mix of simple, prismatic or rotational components and complex components with free-form features. Therefore, the mold design solution must provide comprehensive libraries and an intelligent assembly design module, together with functionality for complex free-form surface design - as in the case of uneven parting lines and complex filleting tasks.

The Part Is the 3-D Reference Basis

Usually the designer begins with a preliminary part design, which means the work around the core and cavity could change. After the calculation of the optimal draft of the part, the position and direction of the cavity, slides and inserts have to be defined. The 3-D system supports the designer with the calculation of a parting line and the segmentation into slides and inserts based on the 3-D model of the part. Moreover, the mold system provides functions for the checking, modifying and detailing of the part. Already in this early stage, drawings and bill of materials can be created automatically.

When choosing the standard mold, the designer can define any size, thickness and number of plates. For example, a mold with two splitting lines or special molds with two ejector systems - one in the moving side and one in the static side - can be created quickly and easily.

When positioning standard components such as ejectors or screws, not only is the geometry of the component itself created, but also the necessary holes. In the case of the ejector pins, the counter-bore, the through-hole and the fit in all of the plates and inserts are affected. The system automatically stores the relationship between the holes and the components. For example, when a screw is moved, the tap in one plate and the counter-sink and the through-hole in other plates are moved with it so there will not be an error in the position of functionally related holes in different plates or inserts.

The possibility to copy, mirror or rotate components or whole sub-assemblies is very important for the efficiency of a CAD system. For example, if you want to design a multi-cavity mold, only one core and cavity has to be designed. All of the others can be created automatically by copying. In a 3-D mold design system this means the whole insert with all of the components that will be copied are selected in one step and then arranged in an array, mirrored or rotated with copying. The system then automatically creates all of the new holes in the plates and all of the new components. The bill of materials then automatically contains the new number of components and the NC table with the new holes.

This not only is possible for fixed standards but also for user components. These are the company's own specific components that are defined by the user and stored in a user standard library. These user components can then be handled with the same logic and functionality as the standard library.

All of these features are provided in a new special 3-D mold design system. The big advantages of this system are:

• Access to three-dimensional standard libraries from certain companies.
• Possibility to create user libraries.
• Automatic creation of drawings and the bill of materials.

Interfaces like IGES, STEP, VDA, DXF and STL (SLA) guarantee optimal connection to other systems. There also are modules for two and a half-, three- and five-axis CNC-programming. Electrode manufacturing and the automation of all of the cycles for the plates guarantee economical advantages. Three-dimensional design systems are available today for all common Windows NT and Unix platforms.

The use of a special 3-D mold design system can shorten development cycles, improve mold quality, enhance teamwork and free the designer from tedious routine work. The economical success, however, is highly dependent upon the organization of the workflow. The development cycles can be shortened only when organizational and personnel measures are taken. The part design, mold design, electrode design and mold manufacturing departments have to consistently work together in a tight relationship.