Visual Controls Improve Quality And Productivity

Maryland Precision Spring/Rolex division of MW Industries manufacturers a wide range of coiled springs, constant force springs, washers and formed metal parts. These products are used in the automotive, medical, power tool, public transit, military, aerospace and energy industries.

One of the company’s major product lines is a series of electric motor brush assemblies used in power tools. These brush assemblies contain a number of small, complex parts that are fabricated in-house and then assembled using the company’s sophisticated automated assembly equipment.

Some time ago, the company’s continuous improvement team looked at the manufacturing process for these brush assemblies. Using value stream mapping, a technique that identifies waste in a process, the team discovered many opportunities for streamlining and improving the process. They found insufficient component identification, which led to part mix-ups; wide swings in component inventory levels (one part had approximately 100 days of inventory on-hand, while another part with the same usage requirement had 2 days of supply on-hand); and insufficient housekeeping practices.

In an effort to improve quality and meet the anticipated increase in brush assembly business, the team decided to make the assembly area more “visual” to allow workers to identify and control components as well as reduce quality problems. For example, although the automated assembly machines were dedicated to various brush assemblies, there was no clear identification as to which component went into which feed hopper for eventual insertion into the assembly. First, photos of each component were affixed to the feed hoppers so anyone could verify that the right components were in the right hoppers. Another step was to obtain color-coded totes to store different components. Finally, as a further means of reducing the chance of component mix-ups, feed hoppers were identified with the same color as the totes that stored the components (components from the red totes went into the red hoppers and so forth).

Once the visuals were in place, the team addressed the unbalanced component inventory issue by establishing a highly visual and relatively simple component supermarket system. This system regulated the quantities of components to ensure that the same number of each was available at any point in time. The supermarket quantities were based on the daily usage rate and the replenishment lead time. For example, if the average daily demand for a component was 20,000 and it took 5 days to produce an order, you would need a supermarket that could hold at least 100,000 of these components. As some of the components were purchased, procurement lead times had to be factored into the supermarket size calculation to prevent stockouts.

In practice, as components are used, the empty totes are delivered to the supplying process (or order cards to the purchasing department) to initiate replenishment. The color coding has been extended to the component supplying process, in this case a four-slide machine department. A color-coded staging area has been established, and the empty totes are placed in the corresponding color section. The empty totes are stacked and machines are set up once the stack reaches a certain height (reorder line).

The results of the continuous improvement team’s efforts have been impressive. The visuals in the assembly cell have contributed to an 80-percent improvement in quality. There are also fewer machine stoppages and jams, which used to occur whenever an operator placed the wrong component in the feed hopper. The supermarkets have helped balance the inventory and keep the company from running out of any components. These improvements, combined with other continuous improvement initiatives, have allowed Maryland Precision Spring/Rolex to increase output of these brush assemblies by 15 percent to meet customer demand.

Interestingly enough, the improvements in the assembly area have generated improvements in the four-slide department as well. Employees from this department recently completed a workplace organization effort. They were able to eliminate much clutter and improve the overall appearance of the department. As Barry Hammacher, the firm’s continuous improvement manager says, “The four-slide workplace organization effort brought an innovation to light. One machine dedicated to production of brass brush assembly components had been raised on steel beams to make setup easier and allow for better housekeeping around the machine. This led to raising all the machines in the department, making everyone’s job easier.”

Another initiative in the works is to improve setup time on the four-slide machines. Reduced setup times will provide greater flexibility and more economical production of smaller batches, which will reduce the component replenishment lead time and inventory levels.