Metaldyne Inc., Plymouth, MI, completed a plant-wide energy assessment recently, at its forging facility in Royal Oak, MI. The assessment team addressed opportunities to increase energy efficiency, reduce waste and pollutants, and increase productivity by evaluating demand-side energy management, best practices, the use of emerging technologies, and potential supply-side improvements.
Although the assessment focused on the plant’s large energy-using systems and equipment, the team also evaluated product inventory and the potential for reducing — or even eliminating — defects, which could also increase the plant’s energy efficiency. Lean manufacturing techniques, best practices, and the use of emerging technologies that could improve plant efficiency were also considered.
According to the assessment team, if all the projects identified during the Royal Oak plant-wide study were implemented, total annual energy savings for electricity would be more than 11 million kWh. Total annual cost savings were estimated to be $12.6 million.
The U.S. Department of Energy’s (DOE) Industrial Technologies Program (www.energy.gov) co-sponsored the assessment through a competitive process. DOE promotes plant-wide energy-efficiency assessments with potential to improve industrial energy efficiency, productivity, and global competitiveness, while reducing waste and environmental emissions. In this case, DOE contributed $100,000 of the total $200,000 assessment cost.
Metaldyne and its assessment team looked for opportunities to increase energy efficiency, reduce waste and pollutants, and increase productivity. Electricity is the plant’s main process-related energy source. Natural gas is used primarily for water heating and for heating, ventilation, and air-conditioning (HVAC) systems, and has a negligible role in process heating.
The assessment team evaluated demand-side energy management, best practices, opportunities for implementing emerging technologies, and potential supply-side changes. The assessment concentrated on the plant’s large energy-using systems and equipment.
This large equipment included the solid-state induction heaters for the Hatebur hot-forging machines, the warm-forging press, the hot-forging vertical press, the Wagner hot ring rollers, electric motors, material handling equipment, HVAC, and lighting.
Product inventory and the potential for reducing or eliminating defects were also examined. Manufacturing processes were examined for potential lean manufacturing/best practices improvements. The assessment team also identified some emerging technologies that could improve manufacturing efficiency.
21 cost-saving projects
As a result of its assessment, the team, comprised of energy and manufacturing process experts, made 21 assessment recommendations (AR). Factoring in process improvements that would result in savings in water and waste production, the Royal Oak plant could save more than $12.6 million annually in overall plant energy and operating costs if all the assessment recommendations were implemented. The cost of implementing all the projects would be approximately $6.5 million. Selected recommendations are discussed below.
Install air-saver nozzles on press-machine blowoff lines — Several of the presses use a continuous stream of compressed air blown through two 3/8-in. open pipes to detach parts from the dies. The assessment team recommended installing air-saver, high-thrust nozzles on the air lines to reduce compressed air usage. Air-saver nozzles work by entraining ambient air into the flow of compressed air.
Install radiation shields and improve insulation to reduce heat losses from induction heaters — Eight multistage induction heaters preheat the bar stock before forging. The air gaps between stages, which allow access for maintenance and temperature measurement, also permit excessive heat losses. The assessment team recommended installing an insulated, removable radiation shield to reduce heat losses through the air gaps. A quartz window could also be installed to allow the bar stock to be inspected visually.
Install a controlled cooling system for parts whose heat treating is currently outsourced — The assessment team recommended that the plant consider options for in-house controlled cooling of forged parts now being outsourced for heat treating. The options were (1) to use a batch-type cooling system, in which parts are placed in bins and cooled under controlled temperature and time conditions immediately after being forged; and, (2) to use a batch-type system to control the cooling of parts produced from the ring rolling machines, and two continuous (spiral) systems to handle single parts produced directly from the Hatebur presses. If cooling bins are used, the batch-type systems should feature high-convection recirculating air flow to ensure uniform cooling of all the parts.
Reduce change-over time for press retooling — Current press change-over times for die replacement are longer than necessary, increasing machine downtime and wasted electricity because the induction heaters remain hot while the machine is idle. The team recommended a list of actions to reduce change-over time, including improving personnel training and procedures, upgrading the tool kit, and using automatic locators for dies.
Reduce product inventory — The team considered the current average stored inventory of one month’s production of finished product to be excessive. The team recommended that the plant reduce its product inventory by 50% by taking the following actions: Producing smaller lot sizes of product for each product type, and setting minimum and maximum inventory levels for each product type. Savings would result from reductions in inventory carrying costs, i.e., those associated with keeping inventory. These include capital costs, taxes, insurance, handling costs, warehouse costs, and damaged inventory.
Establish a “pull scheduling” system — The goal of lean manufacturing is to minimize or eliminate non-value-added steps in the process across the entire product supply, production, and customer delivery cycle. The “pull scheduling” approach ensures that upstream manufacturing activities are linked and controlled by the activities of the next downstream operation. The downstream operation physically sends distinct visual or electronic signals2 to the last upstream operation, directing that operation to respond to its needs for a product or service. This approach, often called “kanban,” is essentially process-driven.
Improve product quality and reduce rework — Currently, product inventory is excessive and parts are stored longer than necessary. As a result, inventory stored outside can experience surface degradation caused by rain. The assessment team recommended reducing product inventory and improving material flow through the plant. These measures would reduce storage time and associated rework on degraded material.
Increase machine tool durability — A new technology that can increase the life of tools and improve the finish of parts involves applying hard coatings made of thin-film nitride or carbide-based ceramics. The assessment team recommended that Metaldyne consider using hard coatings on inserts, drills, bits, and other parts to increase the speed of machining operations, as well as the life of tools. These measures would also reduce press downtime and costs associated with punch and die manufacturing.
Increase punch and die life by applying lubricating coatings — The team recommended that the life of the forging tools (punches and dies) be increased by maintaining cooler tool surfaces. This could be accomplished by reducing the cooling water temperature and by applying a lubricating coating to the tool surface. Longer tool life would increase the productivity of the forging presses, reduce press downtime, increase throughput, and reduce overall production costs.