By Dr Vallury Prabhakar

Stamping dies are a substantial invest-ment for automotive manufacturing in the range of US$ 80-100 million per vehicle programme. Unlike power-train and transmission, which remain relatively unchanged over long periods, stamped parts are continuously evolving for styling. Design standards change to meet stringent targets in performance criteria for fuel efficiency, weight reduction and safety while also adapting to the latest materials and production methods. This results in major re-design of stamping dies for each vehicle programme. 250 model launches worldwide translates into a yearly investment US$10-15 billion for stamping dies. With the growing emphasis on lower-volume niche vehicle programmes by OEMs, this investment will certainly increase. This paper examines core improvements that remain untapped and how these may be sustained with new technology solutions and enterprise workflow refinement.

Life-cycle harmony

The current frenzy on cost reduction - at any price - has largely neglected the impact on quality, lead-time and throughput leading to a higher 'real-cost-per-part'. Due to the relative ease of calculating upfront costs, compared to the lack of ability to project effects on quality, delivery, and morale, this impact goes unnoticed. Further, the time lag between these early decisions and realised impact can be several months or years, which makes closing the loop on these assumptions impossible to track.

 For example, a spot reduction of 15-20 per cent on die-cost may cause an unstable process leading to excessive scrap and unplanned downtime at the plant - far exceeding the intended "savings". Execution of such metrics runs counter-productive, creating profoundly negative impact on market timing, profit margins and long-term relationships for OEMs and suppliers. Over time, this also creates a breakdown of internal team cohesiveness and motivation within the organisation.

A unified vision - fast-to-market production of quality parts at lowest cost - requires the complete life-cycle to be 'harmonious', i.e., reinforce deep collaboration between multiple disciplines of costing, engineering and operations. An orchestrated work culture must be used to drive an enterprise whole that is greater than the sum of its parts. Accurate data and dependencies must be factored into each decision metric. A disciplined adherence to these decisions is needed to look beyond smaller increments for the greater good.

Technology enablers & new concepts

Over the past decade, design and simulation software for metal-stamping has become indispensable in concurrent product and die engineering. For all types of parts including Class A, BIW, structural or hydro-formed, the technology is routinely used to certify part formability, develop a feasible process concept and validate that the process will in fact produce an acceptable part in the press (transfer, line or progressive). The speed and reliability of these tools - designed to complement shop-floor expertise - have dramatically reduced lead-time in engineering change and die-tryout by an acknowledged 50-60 per cent. More importantly, it has produced a revolutionary shift from legacy-based tweaking to a data-driven decision toolkit aligned closely with the die-shop and stamping plant environment.

Technology also augments in-house die expertise especially with the advent of newer materials (high-strength alloys, aluminium, etc), as well as alternative processes such as progressive dies and hydro-forming. Today, tool engineers routinely design and validate 4-5 die-concepts a day on a standard desktop computer (see references 1, 2, 3, 4). The software helps slash raw material costs through blank-reduction and down-gaging studies, which provides significant ROI for high-volume programs. Clearly this technology has become a mainstream necessity for world-class die-making competitiveness.

With this paradigm shift in lead-time reduction and concurrent die development, software vendors have introduced cutting-edge technologies to directly address total cost and quality in the unified vision. These new innovations generate a harmonious balance of all key metrics through an enterprise-wide collaborative effort. These are aligned to four major solutions as follows:

•  Feasibility Solution: Starting with very early 3D data, product and die engineers establish part manufacturability and optimum material utilisation (blank-sizing, nesting). They also initiate a feasible die-process, e.g., binder/addendum development, secondary operations, flange layout, etc., to further refine the stamping process. This solution is characterised by very quick turnaround time and reliability - most parts will run in 5-30 minutes, identifying over 90% of potential forming issues very early.

• Bidding/Planning Solution: The estimating group starts with a process layout (created automatically from the 3D part features) or can import it from the feasibility solution stage. Total die-cost is then calculated from a database of operations, labour hours and material costs. Different press-lines and process sequences can be instantaneously modelled for cost comparison. The cost output accurately reflects a real die-process whose feasibility has already been established.

• Tooling/Tryout Solution: The chosen cost-optimal process from bidding/planning is then further refined by tool engineering for detailed die layout and design. Very precise tryout simulations and process optimisation produce a superior part with acceptable forming (thinning, strains, etc) and dimensional characteristics (springback, impact lines, etc).

•  Robustness Solution: Finally, the baseline die-process in tooling/tryout undergoes a deeper robustness study to highlight and potentially correct part quality issues that could result from real-life plant variances, e.g., blank shift, inconsistent material, lube breakdown, die wear, etc. This is accomplished through a multi-variate simulation study with hundreds of iterations compiled to graphically represent dominant parameters and their quantitative influence on part quality. This portfolio of solutions integrates seamlessly with each other via an underlying data-structure that is continuously updated and maintained. This allows for consistent data-driven decisions using objective and refined 'across-the-board' information. Over and above the lead-time improvements discussed earlier, there are several compelling benefits in this enterprise technology method, namely:

1)  It allows the freedom from having to solely rely on experience-based standards that may become obsolete by not reflecting newer criteria, materials and methods.

2)  The common 'tweak-and-check' approach to die engineering that yields unsustainable improvements is fully replaced by a state-of-the-art discipline of virtual engineering producing the lowest 'real-cost-per-part' for every part and every time.

3)   True die and production costs can be compared to an enterprise wide costing structure closing the loop between estimates and reality. Process decisions and can be reviewed at every phase for impact on quality, cost and delivery of the finished product.

Summary

Virtual die technologies embraced in the past decade have grown by quantum leaps. However, this continues to be limited to the small (but important) subset of tool engineering, with little or no vision to enterprise standards. In between the resultant pockets of localised efficiency, there is still a large vacuum in which much of the enterprise gains remain untapped. Senior management at many OEMs and suppliers have become true champions for sustainable excellence by driving technology-refined work-culture deep within the hearts of their organization. The early adapters of are already starting to realise superiority in competitiveness, productivity and profit margins with no compromise. This holistic approach, from product concept to full production within a contiguous environment, allows the forward thinking enterprise to chart its brighter future, while discarding a legacy of history-based decisions to become the new benchmark of manufacturing excellence.

References

[1] "Volvo Cars - Form and Function", International Sheet Metal Review, May/June 2006.

[2] "Die Design and Build: Virtually Faster", Stamping Journal, Vol. 17, No. 7, July 2005.

[3] "Robust Engineering", International Sheet Metal Review, September/October 2004.

[4] "Die Design and Validation Software - Seeing is Believing", Metalforming Magazine May 2004.

About the author

Dr Vallury Prabhakar (vallury@ autoform.com) is the CEO of AutoForm Engineering USA, Troy, Michigan (www.autoform.com) since 2001 and is responsible for all operations in North America including sales, support and consulting. Prior to this position, Dr Prabhakar worked at GM as engineering manager for math-based manufacturing. The author is thankful to Kidambi Kannan, Eric Kam and Oliver Goronzy for their help and contributions in this article. AutoForm India Office is in Hyderabad. (E-mail info@autoform.in and Tel: 040-66848636).