Case Study: Successful Transition from Open to Closed Die Forging in Heavy Industry

In heavy industry, forging is a cornerstone process for producing high-strength, durable components used in sectors such as aerospace, automotive, mining, and energy. For decades, open die forging dominated many factories due to its simplicity, flexibility, and lower capital requirements. However, as market pressures intensified—driven by the need for tighter tolerances, complex geometries, and leaner operations—a growing number of heavy manufacturers have completed a strategic shift to closed die forging. This case study examines one company’s journey from open to closed die forging, the technical and operational changes involved, and the measurable benefits achieved.

The transition from open to closed die forging is not merely a change in equipment; it represents a fundamental rethinking of the entire manufacturing workflow. By examining real-world challenges and solutions, this article provides a blueprint for other heavy industry players considering the same move. For a broader introduction to forging methods, see the Forging 101 overview from Industrial Heating.

Understanding Open and Closed Die Forging

Open Die Forging: Flexibility Meets Limitations

Open die forging, also known as “smith forging,” involves hammering or pressing a heated metal workpiece between flat or simple contoured dies that do not fully enclose the material. The operator manually positions the workpiece to achieve the desired shape. This process is highly flexible—any size or shape can be approximated with proper skill—and tooling costs are low. Typical applications include large shafts, rings, and custom components that require only general dimensional accuracy.

However, open die forging has inherent drawbacks. Without a closed die cavity, the material flows largely uncontrolled, often leading to excess flash, inconsistent grain structure, and significant post-forging machining. Material utilization is poor; scrap rates can exceed 30% on complex parts. Dimensional repeatability depends heavily on operator skill, making it difficult to maintain tight tolerances across production runs.

Closed Die Forging: Precision and Efficiency

Closed die forging, also called impression die forging, uses a set of dies that completely encase the workpiece. The material is forced into the die cavity under high pressure, taking on the exact shape of the cavity with minimal flash. This method delivers superior dimensional accuracy, repeatable grain flow, and excellent surface finish. Almost no secondary machining is required, drastically reducing material waste and cycle time.

Tooling costs are significantly higher—dies can be expensive to design and fabricate—but per-part costs drop dramatically for medium to high production volumes. Closed die forging is the preferred method for components like connecting rods, gears, turbine blades, and intricate brackets where strength-to-weight ratio and precision are critical.

To dig deeper into the technical distinctions, the Forging Industry Association’s resource on forging types provides a comprehensive comparison of processes.

The Drivers for Change in Heavy Industry

The company at the center of this case study—a medium-sized manufacturer of heavy equipment components—had relied on open die forging since its founding. By the late 2010s, several external and internal factors converged, making the transition to closed die forging not just desirable but essential for survival.

Market Demand for Higher Precision

Customers in the mining and energy sectors began specifying tighter tolerances (±0.5 mm on critical dimensions) and more complex geometries that were impossible to achieve consistently with open die forging. The company was losing bids to competitors who already offered closed die capabilities.

Cost Pressures and Waste Reduction

Raw material costs, particularly for high-alloy steels and nickel-based superalloys, had risen sharply. Open die forging generated 25–35% scrap due to flash and post-forging machining. Management calculated that reducing waste by even 15% would yield annual savings exceeding $500,000.

Quality Consistency and Traceability

Automotive-tier and aerospace customers demanded certified, repeatable processes with full traceability. Open die forging’s operator-dependent quality made it difficult to implement statistical process control (SPC) and meet ASQ SPC standards for continuous improvement.

Production Throughput

Open die forging required multiple reheats and manual repositioning for each part, limiting output to 8–10 parts per shift on complex items. Closed die forging promised cycle times of under 3 minutes per part after setup, dramatically increasing capacity without expanding floor space.

Planning the Transition: Technical and Operational Considerations

Equipment Selection and Capital Investment

The company evaluated several hydraulic press configurations, ultimately selecting a 2,500-ton press with programmable controls and fast-acting hydraulics capable of handling the largest die sets anticipated (up to 1,200 mm footprint). The investment also included die preheating ovens, an automated lubrication system, and a robotic part handler to reduce cycle time and improve ergonomics. Total capital outlay was approximately $8.2 million.

A critical decision was whether to purchase standard die sets or invest in customized tooling. The team chose to partner with a die engineering firm to design modular tooling families that could be adapted to multiple part numbers with minor inserts. This approach reduced die changeover time from an estimated 4 hours to under 45 minutes.

Process Redesign and Simulation

Before commissioning the new press, the engineering team ran finite element analysis (FEA) simulations for the five most complex parts in the product lineup. These simulations validated die cavity designs, predicted material flow, identified potential forging defects (laps, folds, and underfills), and optimized flash-land geometry. The company used Simufact Forming, a leading forging simulation package, to iterate on die designs without costly physical prototyping.

Pilot runs for each part followed the simulation phase, using temporary die inserts to fine-tune preform dimensions, forging temperature (1,100–1,200°C for alloy steels), and dwell time. Three parts required one additional die iteration; all five met dimensional specifications by the second pilot run.

Workforce Training and Culture Change

Perhaps the most challenging aspect was training the workforce. Open die forging relies heavily on the “hammer man’s” skill and intuition. Closed die forging demands discipline—die setup precision, process parameter adherence, and rigorous quality checks. The company implemented a four-phase training program:

  • Phase 1: Classroom instruction on forging metallurgy, die design principles, and press controls (40 hours).
  • Phase 2: Virtual reality simulations of die setup and part loading/reloading (20 hours).
  • Phase 3: Hands-on training on a dedicated training press with simple flat dies (60 hours).
  • Phase 4: On-the-job coaching during pilot production runs, with senior operators mentoring junior staff (120 hours).

Resistance to change was initially strong—some veteran operators believed closed die forging would “de-skill” the trade. Management addressed this by communicating that the transition would create new, higher-value roles in die design, process engineering, and quality verification. Within six months, operator buy-in improved significantly as they saw the reduced physical strain and more predictable work pace.

Material Handling and Forging Flow

Closed die forging imposes different material flow constraints. For example, the start billet volume must be precisely controlled; too much material produces excessive flash that can cause die lock-up or surface defects. The company invested in a laser-based billet weighing and trimming system that cut billets to within ±0.5% of target volume. Preheating was standardized to a uniform 30-minute soak at 1,150°C using a regenerative gas furnace with a ±5°C zone control.

Implementation: From Pilot to Full-Scale Production

Phase I: Single-Part Qualification (Months 1–3)

The first part selected for closed die forging was a low-alloy steel bracket previously produced by open die forging with 40% material waste. After three pilot runs and two die modifications, the part achieved 98% first-pass yield in production. Material waste dropped to 8% (only flash and one small return-to-billet trim operation). Cycle time decreased from 12 minutes per part (including two reheats) to under 4 minutes per part (single heat, automatic part handling).

Phase II: Line Expansion (Months 4–8)

With one part qualified, the team expanded to the remaining four high-volume parts. Each required its own die set and optimized preform geometry. The modular die design paid off: changeovers between part families averaged 35 minutes. By month eight, the closed die line was running two shifts, producing 800 parts per day—three times the output of the equivalent open die line.

Phase III: Scaling to Full Product Line (Months 9–14)

The final push involved converting lower-volume parts (under 50 units per year) to closed die forging. Because tooling costs per part were high for low volumes, the company implemented a “die rental pool” for common shapes (prismatic blocks, stepped shafts) with shared die inserts. This approach reduced tooling cost per part by 60% for volumes under 100 units annually.

By month 14, 85% of the company’s forging volume was produced using closed die methods. Only extremely large parts (over 1,500 mm length) and one-off prototypes remained on open die presses, which were repurposed as backup for breakdowns and specialty orders.

Measured Results and Benefits

Quantitative Improvements

One year after the full transition, the company reported the following metrics compared to the baseline open die operation:

  • Material waste reduction: 22% (from 32% to 10% average scrap rate).
  • First-pass yield improvement: from 70% to 95%.
  • Cycle time reduction (weighted average): 65% (from 15 minutes to 5.25 minutes per part).
  • Post-forging machining reduction: from 20 minutes per part to 2 minutes (minimal cleanup).
  • Operator productivity: parts per operator per shift increased 220%.
  • Energy consumption per part: down 40% due to fewer reheats and shorter press cycles.
  • Customer rejections: decreased by 85%.

Qualitative Benefits

  • Enhanced brand reputation: The company became a preferred supplier for three OEMs that previously sourced only from closed die forges.
  • Reduced operator fatigue and injuries: Robotic material handling eliminated heavy manual lifting of hot billets (up to 40 kg).
  • Improved process data: The new press generated real-time force, temperature, and speed data that fed into the SPC system, enabling predictive maintenance and process optimization.
  • Environmental impact: The 22% reduction in scrap plus lower energy consumption reduced the company’s carbon footprint by an estimated 150 metric tons of CO₂ per year.

Lessons Learned and Future Opportunities

Key Success Factors

  • Top management commitment: The CEO personally championed the project and allocated a contingency fund for unseen issues.
  • Phased implementation: Starting with one validated part reduced risk and allowed the team to refine processes before scaling.
  • Investing in training and simulation: These upfront costs avoided costly mistakes during production.
  • Close supplier collaboration: The press manufacturer and die designer were embedded in the project team, ensuring seamless integration.

Challenges Encountered

  • Initial die life was shorter than expected: Lapping and surface polishing regimens needed adjustment after early dies wore prematurely (30,000 parts instead of 50,000). Working with the die supplier to optimize steel grade (H13 tool steel with nitriding) extended life to over 60,000 parts.
  • Flash variability: Even with precise billet weight control, flash thickness varied by ±0.3 mm, causing occasional die misalignment. The team implemented a flash trimming station with automatic feedback to the press operator.
  • Cultural resistance: Veteran employees needed up to a year to fully adapt. Regular town hall meetings and a “best operator” award helped shift attitudes.

Next Steps

Encouraged by the results, the company is now evaluating hot isostatic pressing (HIP) for a small subset of high-alloy parts and exploring closed die forging with near-net-shape capability to further reduce machining. The engineering team also plans to implement a digital twin of the forging cell, linking real-time sensor data to a CAD model for instant process deviation alerts.

For heavy industry manufacturers still on the fence, this case demonstrates that the transition from open to closed die forging, while capital-intensive, yields measurable returns in quality, efficiency, and competitiveness within 18 months. The key lies in rigorous planning, workforce engagement, and a willingness to embrace new technologies—from simulation software to robotic handling. As the industry moves toward Industry 4.0, closed die forging becomes not only a production method but a platform for continuous improvement and data-driven decision-making.

Conclusion

The successful transition from open to closed die forging is a transformative journey that challenges a company’s technical, cultural, and financial boundaries. This case study outlines a path taken by one heavy industry manufacturer—driven by market demands for precision, cost reduction, and quality consistency. By investing in the right equipment, simulation tools, and a comprehensive training program, the company achieved a 22% reduction in material waste, 65% faster cycle times, and a dramatic improvement in customer satisfaction.

Any heavy manufacturer considering a similar transition can draw on these lessons: start small, leverage simulation, partner with expert suppliers, and invest in your people. The rewards of closed die forging extend far beyond the press room—they position a company for long-term growth in an increasingly competitive global market. For further reading on forging technology trends, the Thomas Guide to Forging Processes offers a wealth of comparison data.