The Conversion Cycle:Techniques and Technologies That Promote Lean Manufacturing

Techniques and Technologies That Promote Lean Manufacturing

Modern consumers want quality products, they want them quickly, and they want variety of choice. This demand profile imposes a fundamental conflict for traditional manufacturers, whose structured and inflexible orientation renders them ineffective in this environment. In contrast, lean companies meet the challenges of modern consumerism by achieving manufacturing flexibility. This section examines techniques and technologies that lean manufacturing firms employ to achieve manufacturing flexibility.

PHYSICAL REORGANIZATION OF THE PRODUCTION FACILITIES

Traditional manufacturing facilities tend to evolve in piecemeal fashion over years into snakelike sequences of activities. Products move back and forth across shop floors, and upstairs and downstairs through different departments. Figure 7-14 shows a traditional factory layout. The inefficiencies inherent in this layout add handling costs, conversion time, and even inventories to the manufacturing process. Further- more, because production activities are usually organized along functional lines, this structure tends to create parochialism among employees, promoting an us-versus-them mentality, which is contrary to a team attitude.

A much simplified facility, which supports flexible manufacturing, is presented in Figure 7-15. The flexible production system is organized into a smooth-flowing stream of activities. Computer-controlled machines, robots, and manual tasks that comprise the stream are grouped together physically into factory units called cells. This arrangement shortens the physical distances between the activities, which reduces setup and processing time, handling costs, and inventories flowing through the facility.

AUTOMATION OF THE MANUFACTURING PROCESS

Automation is at the heart of the lean manufacturing philosophy. By replacing labor with automation, a firm can reduce waste, improve efficiency, increase quality, and improve flexibility. The deployment of automation, however, varies considerably among manufacturing firms. Figure 7-16 portrays automation as a continuum with the traditional manufacturing model at one end and the fully CIM model at the other.

Traditional Manufacturing

The traditional manufacturing environment consists of a range of different types of machines, each con- trolled by a single operator. Because these machines require a great deal of setup time, the cost of setup must be absorbed by large production runs. The machines and their operators are organized into functional departments, such as milling, grinding, and welding. The WIP follows a circuitous route through the different operations across the factory floor.

Islands of Technology

Islands of technology describes an environment in which modern automation exists in the form of islands that stand alone within the traditional setting. The islands employ computer numerical controlled (CNC) machines that can perform multiple operations with little human involvement. CNC machines contain computer programs for all the parts that are manufactured by the machine. Under a CNC configuration, humans still set up the machines. A particularly important benefit of CNC technology is, however, that little setup time (and cost) is needed to change from one operation to another.

Computer-Integrated Manufacturing

Computer-integrated manufacturing (CIM) is a completely automated environment with the objective of eliminating non–value-added activities. A CIM facility makes use of group technology cells composed of various types of CNC machines to produce an entire part from start to finish in one location. In addi- tion to CNC machines, the process employs automated storage and retrieval systems and robotics. CIM supports flexible manufacturing by allowing faster development of high-quality products, shorter produc- tion cycles, reduced production costs, and faster delivery times. Figure 7-17 depicts a CIM environment and shows the relationship between various technologies employed.

AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (AS/RS). Many firms have increased productivity and profitability by replacing traditional forklifts and their human operators with automated storage and retrieval systems (AS/RS). AS/RS are computer-controlled conveyor systems that carry raw materials from stores to the shop floor and finished products to the warehouse. The operational advantages of AS/RS technology over manual systems include reduced errors, improved inventory control, and lower storage costs.

ROBOTICS. Manufacturing robots are programmed to perform specific actions over and over with a high degree of precision and are widely used in factories to perform jobs such as welding and riveting. They are also useful in hazardous environments or for performing dangerous and monotonous tasks that are prone to causing accidents.

COMPUTER-AIDED DESIGN (CAD). Engineers use computer-aided design (CAD) to design better products faster. CAD systems increase engineers’ productivity, improve accuracy by automating repetitive design tasks, and allow firms to be more responsive to market demands. Product design has been revolutionized through CAD technology, which was first applied to the aerospace industry in the early 1960s.

CAD technology greatly shortens the time frame between initial and final design. This allows firms to adjust their production quickly to changes in market demand. It also allows them to respond to customer requests for unique products. The CAD systems often have an interface to the external communication network to allow a manufacturer to share its product design specifications with its vendors and customers. This communications link also allows the manufacturer to receive product design specifications electronically from its customers and suppliers for its review. Advanced CAD systems can design both product and process simultaneously. Thus, aided by CAD, management can evaluate the technical feasibility of the product and determine its ‘‘manufacturability.’’

COMPUTER-AIDED MANUFACTURING (CAM). Computer-aided manufacturing (CAM) is the use of computers to assist the manufacturing process. CAM focuses on the shop floor and the control of the physical manufacturing process. The output of the CAD system (see Figure 7-17) is fed to the CAM system. The CAD design is thus converted by CAM into a sequence of processes such as drilling, turning, or milling by CNC machines. The CAM system monitors and controls the production process and routing of products through the cell. Benefits from deploying a CAM technology include improved process productivity, improved cost and time estimates, improved process monitoring, improved process quality, decreased setup times, and reduced labor costs.

Value Stream Mapping

The activities that constitute a firm’s production process are either essential or they are not. Essential activities add value; nonessential activities do not, and should be eliminated. A company’s value stream includes all the steps in the process that are essential to producing a product. These are the steps for which the customer is willing to pay. For example, balancing the wheels of each car off the production line is essential because the customer demands a car that rides smoothly and is willing to pay the price of the balancing.

Companies pursuing lean manufacturing often use a tool called a value stream map (VSM) to graphically represent their business processes to identify aspects of it that are wasteful and should be removed. A VSM identifies all of the actions required to complete processing on a product (batch or single item), along with key information about each action item. Specific information will vary according to the process under review, but may include total hours worked, overtime hours, cycle time to complete a task, and error rates. Figure 7-18 presents a VSM of a production process from the point at which an order is received to the point of shipping the product to the customer. Under each processing step, the VSM itemizes the amount of overtime, staffing, work shifts, process uptime, and task error rate. The VSM shows the total time required for each processing step and the time required between steps. It also identifies the types of time spent between steps such as the outbound batching time, transit time, and inbound queue time.

The VSM in Figure 7-18 reveals that considerable production time is wasted between processing steps.

In particular, the transit time of raw materials from the warehouse to the production cell contributes significantly to the overall cycle time. Also, the shipping function appears to be inefficient and wasteful, with a 16 percent overtime rate and a 7 percent error rate. To reduce total cycle time, perhaps the distance between the warehouse and production cell should be shortened. The shipping function’s overtime rate may be due to a bottleneck situation. The high error rate may actually be due to errors in the upstream order-taking function that are passed to downstream functions.

Some commercial VSM tools produce both a current-state map and a future-state map depicting a leaner process with most of the waste removed. From this future map, action steps can be identified to eliminate the non–value-added activities within the process. The future-state VSM thus is the basis of a lean implementation plan. VSM works best in highly focused, high-volume processes in which real benefit is derived from reducing repetitive processes by even small amounts of time. This technique is less effective at eliminating waste in low-volume processes in which the employees are frequently switched between multiple tasks.