Tooling and Materials
The Tooling and Materials work group considered aspects of materials in the forging process, including the materials used in production equipment (die blocks, etc.), new materials to be forged, and the impact of these materials on the forging process. In particular, the group was challenged to consider how to improve the performance and reduce the cost of die systems and improve overall material utilization. To a lesser extent, the group considered what types of materials and parts (powder metals, semi-solid, squeeze casting, etc.) will seriously compete with traditionally forged components and what new forging materials or technologies might create a competitive advantage.
The members of the Tooling and Materials work group represented a rich cross-section of experience and knowledge in dies and materials. The Group had good representation from forging companies, equipment suppliers, national laboratories, and universities. The forging companies that were represented serve several markets including automotive and aerospace, and have experience forging various metals (steel, aluminum, etc.).
The work group reviewed the strategic targets for tooling and material utilization as listed in the Forging Industry Vision of the Future (Exhibit 3-1). The targets appear reasonable as long-term goals although many separate technology advances may be needed to achieve certain targets. There was some discussion of the definition of raw materials; it was concluded that it refers mainly to the material being forged and not die materials and lubricants. It was noted that the targets for tooling and materials are interrelated and are also related to other forging targets, particularly in productivity and quality.
The ability to improve tooling and increase materials utilization is hindered by technology barriers that exist in several aspects of the forging process (Exhibit 3-2). These include lubrication, material property understanding, validated process modeling, measurement and testing, die making, die materials, and process control. Distinctions among these areas are fairly clear, although some barriers associated with measurement and testing, process control, and process modeling may be closely related.
Among the most critical barriers is the lack of effective lubrication methods between the die and the forged material. More precisely, there is a lack of technologies?innovative die materials, coatings, equipment, and processes?that would eliminate the need for lubricants altogether. Material-surface coatings are needed that provide very low heat transfer and can handle variability in the coefficient of friction. There is also inefficient use of lubricants because they are not applied locally to the portion of the tooling or under specific conditions that require lubrication.
Limitations in the area of validated process modeling span a wide range of needs. For example, there is a lack of universal geometrical models, understanding of tribological phenomena, materials models to predict microstructure, cost models to determine minimum cost processes, and other data and methods that could improve modeling of the forging process. The greatest need, however, is in the integration and optimization of these models. In particular, there is a lack of integrated computer systems for forging that take into account all of the relevant process variables. Better integration is needed between the customer's CAD/CAM system, the forge shop's CAD/CAM system, tool design, and other design and process steps to effectively simulate the forging process and adjust part and die design based on this. The cost and the complication of developing and using 3-D simulation tools has resulted in a lack of efficient 3-D computational tools that could greatly improve process modeling. Furthermore, simulations are currently limited in their ability to depict actual conditions. For example, a single friction factor is currently used in simulations of hot forging even though actual friction is known to vary with temperature and materials.
Without integrated, validated process models, it is difficult to determine the optimal die design or material for the product requirement. A sophisticated model could reverse engineer the die and tooling based on the customer part specification and provide an optimal design that uses materials and tools more efficiently.
Effective and efficient process modeling is also linked to better process control. As the industry moves toward precision forging, there is a need to more precisely control the volume and surface conditions of the incoming material. Integrated process control is needed to allow the forger to understand the interrelationship of the process variables and be able to quickly control them depending on current operating conditions.
Other key barriers include the need for better measurement and testing in the forging process leading to the accumulation of forging process data for evaluation; limitations in die materials such as the ability to effectively determine material composition and select appropriate die materials; and limitations in die making such as the need for high speed machining of the die cavity and surface hardening technology.
|Exhibit 3-2. Major Technology Barriers to Achieving Targets
in Tooling and Materials
( = Most Critical Barriers)
|Measurement and Testing||Validated Process Modeling||Material Property Understanding||Die Materials and Die Making||Lubrication||Process Control of Product Materials|
|Real-time non-destructive testing
Lack of use of passive sensors
Limit forging load
Need for cost-effective process monitoring
Accurate non-contact dimensional measurement
Consistent bar billet temperature
We do not know when the die is dead
Accumulating forging process data for evaluation
|Lack of integrated computer system for forging
- customer CAD/CAM FEM forger CAD/ CAM tool design CNC CMMpart
Lack of 3-D, efficient computational tools
Current simulations do not represent actual conditions
Die design optimization - reverse engineering
Heat transfer and conductivity issue
Accurate description of all forging parameters
Smarter systems to optimize tool making cycle (part-to-part)
Ability to simulate part on the forging equipment you are using
Lack of materials models to predict microstructure evolution
Lack of universal geometrical model for forger
Cost-effective system - minimum cost to meet requirements
Lack of understanding of tribological phenomena
|Common descriptor for die steels
Accurate material database to drive simulations
- flow stress vs. temperature data as a function of strain rate for models
Design alloy for forging process
Determine the effect of residual stress on the forging process
Steel which is very ductile at 700ºF, but still good when cooled to right temperature
1. net shape
3. hog-out vs.
|Die material composition and selection
Composite die materials
Surface engineering, thermal heating, and local engineering of surface
Alloys with material properties needed for extended die life are costly to machine
Obtaining a die support material that is stiff enough
High-speed machining of die cavity size and finish
Net shape cavity by forging, casting, semi-solid, and powder
Cutting tool life
Surface hardening technology
|Lack of novel die materials, coatings, and equipment processes that will eliminate lubrication
The lack of condition-specific, targeted lubrication
Lack of material-surface coatings with
1. very low
2. variability of
Better understanding of interface and coating
|Maintaining consistent die temperature
Raw material, control: size, volume, and surface
Lack of first part - good part. No trial and error
Lack of inexpensive and efficient die heating system for isothermal forging
Lack of integrated, instantaneous process control
Focused investments in tooling and materials research can help overcome many of these technical barriers. A balanced portfolio of research in the areas of process analysis, software and process data, die materials and die making, tribology and lubrication, and product material control is needed. The research portfolio should include a mix of near-, mid-, and long-term projects pursued by individual companies, industry collaborations, and government-industry R&D partnerships. Much of the mid- and long-term research requires a collaborative effort between the forging industry and the government in order to be successful. By contrast, many of the near-term research activities can be accomplished by individual companies or companies working in collaboration with other forgers or vendors and customers. Priority research needs are summarized and discussed in Exhibit 3-3 and below.
Die Materials and Die Making
The highest priority research for die making and materials is the development of a multi-attribute, heterogeneous die that eliminates the need for lubricants. This would be an engineered die that would have different material characteristics in various parts of the die to match the specific performance requirements of that area. This would provide greater wear resistance in areas that have a lot of material movement across them and would minimize friction and lubrication needs. Development of such a die could be possible within ten years if supported by a government-industry R&D partnership.
Another research approach to extend die life is to develop coating and cladding of the die material. This research is considered a near-term priority that would require some form of industry consortia or government-industry partnership. Mid-term research that would support both of these needs is better characterization of the materials used in forging dies.
Significant reduction in cycle times to produce forgings can be achieved through the 24-hour turnaround time to produce dies (design, produce dies, and verify).
Tribology and Lubrication
Die life is largely a function of friction, wear, strength, and fatigue resistance which can be mitigated by proper understanding of tribology and the effective use of lubricants. An important element of this is to understand and measure the dynamic conditions that occur at the die-part interface. Related to this is the need to develop a validated model for establishing the sources and characteristics of friction in the forging system. Both research activities are considered to be sufficiently complex and long-term to require an R&D partnership between industry and government to move forward. Supporting research includes a more complete understanding of the physical and metallurgical effects of temperature, pressure, and abrasion on tool materials.
Better measurement, analysis, and control of the forging process will enable operators to increase the consistency of forgings and reduce material scrap rates. The most important research in this area is to develop robust sensors and controls to monitor and control forging equipment. This research could be completed within three years through a government-industry partnership. Another important research activity is to quantify the effects of process variables on finished forgings. For example, it is important to know what effect changes in the temperature of the material or the steel volume of the billets will have on the finished forging.
|Exhibit 3-3. Tooling and Materials Research Needs
( = Top Priority; = High Priority; = Medium Priority)
(I = Proprietary/Company, I/I = Industry Collaboration, G/I = Government/Industry)
|Time Frame||Die Materials and Diemaking||Tribology and Lubrication||Process Analysis||Software and Process Data||Product Material Control|
|Develop coating and cladding of die material
Develop die machining models (e.g., how fast, etc.)
Develop cutting tools to effectively cut advanced alloys
Understand and model the induction process (hardening) (die surfaces)
|Determine the effects of different types of scale on die surface
|Develop robust sensors and controls to control forging equipment
Quantify effects of process variables on finished forgings
Develop real-time non-destructive measurement systems
Model residual stress and NDTE of stress patterns
|Design PC-based neural network reverse engineering model
Develop forging-specific CAD-CAM system
Develop coupled 3-D models of forging process (die and piece) on massively parallel machines
Improve models to predict microstructure
|Require more consistent materials
- flow stress from supplies
Pursue joint company vendor research projects
|Develop multi-attribute, heterogeneous die that eliminates lubrication
Characterize materials used in forging dies in die materials
|Develop techniques to measure exact loading of dies press
Understand and measure the effect of design and process variables on the forging to achieve "first piece - good piece" techniques
Develop non-destructive measurement techniques of the real-time temperature profile of the billet during induction heating
|Develop computer systems that can forward and reverse engineer with link to customer/designer
- link with customer-designer
|Develop validated models for establishing friction in the forging system
Improve friction wear and materials models
|Develop die material model based on composition of material
- predict interface characteristics
Develop models that can handle parametric studies for cost optimization
- die material
|Understand and measure the dynamic conditions of the die-part interface
Understand physical and metallurgical effects of temperature, pressure, and abrasion on tool materials
|Create a centralized data bank
- examine, gather, and apply materials property information from other industries
Develop design optimization software for 24-hour tooling
Develop a flow stress database for use in model simulations
Develop a system to accurately model forging based on material characteristics
Validate process models to simulate actual conditions
Real-time non-destructive measurement systems must be developed for the forged product, the die, and the press. Such systems will enable an operator to determine important process conditions such as temperature, dimension characteristics, and filling of the cavity. Non-destructive testing is also needed for evaluating stress patterns that will enable modeling of residual stress in the forged product. Both activities are considered to be near-term research projects that will require government-industry interactions.
One area that deserves additional attention is the need to understand and measure the effect of process variables on the forging to obtain "first piece, good piece". This concept would ensure sufficient understanding and control of the process to design and engineer a forging system that will produce a quality forging the first time steel is put into a die. This could greatly improve material utilization and help reduce scrap rates.
Software and Process Data
The development of validated computer models and the underlying process data that go into them is one of the most important research priorities for improving tooling and materials utilization. The most critical research need is to develop optimization software for die design that would enable 24-hour tooling. This will require the development of a centralized data bank of materials property data that can be gathered from other industries and applied to forging operations. The data bank could be made Internet-accessible for widespread use. There is currently a lack of flow stress data that is needed to develop better model simulations. All activities are expected to require ongoing efforts that will produce useful results in the near-, mid-, and long-term and will require government-industry collaboration.
Four research areas were identified in which government participation may not be needed to improve modeling because they may be successfully accomplished through industry collaborations. These research activities include validating process models to simulate actual operating conditions, developing models that can handle parametric studies of cost optimization, developing a forging-specific CAD/CAM system, and developing a computer system that can forward and reverse engineer a forged part. This last item would directly link the customer with the designer and speed the part design and delivery while lower cost.
Other important research priorities include developing a die material model based on the composition of the materials and improving materials models to predict microstructure.
Product Material Control
Better material utilization can be achieved by improving the quality and consistency of incoming materials. Although this may not require new research, better communications and interactions with suppliers can improve the consistency of incoming materials, particulary flow stress characteristics. Joint research or quality management initiatives between companies and vendors could go a long way to improving the overall utilization of raw materials.