How to Improve Manufacturing Efficiencies

A little analysis can often yield significant improvements without adding significant capital or labor costs
By Pete Williams, Chelsea Building Products
September 15, 2000
FEATURE ARTICLE | Operations

 

 

In looking at how to improve manufacturing efficiencies, there are a number of questions you need to ask yourself. Do you have control of the manufacturing process? Is your labor cost at what it should be or is it too high? Is your manufacturing running at peak efficiency? Is your manufacturing process running at peak capacity? Do you need to add manufacturing equipment?
Often, adding manufacturing equipment is necessary, but it is equally important to understand the many other steps that you can take to improve manufacturing production and efficiency:

 

  • Balance the production line to the bottleneck, or the one operation within your production that controls the amount of product that can be produced in one shift, regardless of all other work stations. An example could be a two-point welder with a 3 minute cycle time. It can produce 20 squares per hour, that is the limit, regardless of the number of sash that you can glaze.
  • Combine duties to even out work elements.
  • Keep work stations close together to minimize material handling.
  • Eliminate unnecessary or unproductive work.
  • Keep work-in-process inventory to a minimum.
  • Maintain equipment to insure quality and efficiency.
  • Cross train employees for multiple jobs.

There are two ways to reduce labor costs without capital expense. The first is to eliminate production employees while maintaining the same production levels. The second is to increase productivity using the same employees. By focusing on labor costs and production capacity, this article is designed to offer manufacturers ideas using both approaches. We will also take a closer look at two production lines, suggesting potential areas of improvement within one and, in the other, highlighting the benefits of taking a “cellular manufacturing” approach.

Line Efficiency versus Machine Efficiency

To begin finding ways to maximize manufacturing production and efficiency, a number of concepts are helpful to analyze current operations. The first idea is to measure line efficiency, which is the standard time for each process in a production line added together then divided by the actual time it takes for a product to cycle through the line. The following example demonstrates how the line efficiency is determined for a simple three station production line:

 Station OneStation TwoStation Three 
Standard.50.25.40=1.15 minutes
Actual.50.50.50=1.50 minutes

At Station Two, .25 minutes is lost waiting for Station One. At Station Three, .10 minutes is lost waiting for Station Two. Line efficiency in this case is 1.15 minutes (standard) divided by 1.50 minutes (actual), which equalts 76.67 percent. Line efficiency should run at 80 to 90 percent to be cost effective.
Machine efficiency is the time a machine actually runs versus the total time it is available. As an example, one machine runs 1.50 minutes to process one part, but waits for the operator to load/unload or get material, etc., for an additional 1.50 minutes. Machine efficiency is 1.50 minutes to process divided by 3.00 minutes total or 50 percent efficiency.

How to Balance a Line

Understanding these ideas provides the basis for determining how to balance a production line to a bottleneck. If we look again at the example shown above for line efficiency, we see that our line efficiency of 76.67 percent and our production capacity is 60 minutes per hour divided by.50 minutes per unit is 120 units per hour. If we combine duties of Station Two and Station Three into a one person operation, we see the following change in line efficiency:

 Station OneStation Two 
Standard.50.65=1.15 minutes
Actual.50.65=1.30 minutes

Now, .15 minute is lost waiting at Station One, but line efficiency is 1.15 min (standard) divided by 1.30 min. (actual) or 88.5 percent. Production capacity is 60 minutes per hour divided by.65 minutes per unit, which equals 92 units per hour.
With this change, the labor cost is lower, but so is production capacity. A manufacturer needs to ask if 92 units per hour is going to provide the volume that is needed?
If a third person is added to station one to cut the job in half or double its capacity, then station three becomes the bottleneck:

 Station One (A,B)Station TwoStation Three 
Standard.25 + .25.25.40=1.15 minutes
Actual.40 + .40.40.40=1.60 minutes

Line efficiency is 1.15 minutes (standard) divided by 1.60 minutes (actual) or 71.9 percent. Production capacity is 60 minutes per hour divided by.40 minutes per unit or 150 units per hour
Now, capacity is up by 30 units per hour, (a 150 versus 120 or a 25 percent increase), but labor is up 33 percent (from 3 to 4 people).
What if we can take .10 minutes of work from Station One and add this to Station Two:

 Station One (A,B)Station TwoStation Three 
Standard.40.35.40=1.15 minutes
Actual.40.40.40=1.20 minutes

Line efficiency becomes 1.15 minutes (standard) divided by 1.20 minutes (actual) or 95.8 percent. Production capacity is 60 minutes per hour divided by .40 minutes per unit or 150 units per hour
Now, we are producing the same amount of product with three people as we were with four people in the example above.
There are a number of indicators you can see on the plant floor which should tell you where there is room for improvement. Look at each operation within the manufacturing line to see:

  • Is work in process piling up between work stations?
  • Are employees waiting on product to get to their station?
  • Are employees pacing themselves because their operation takes less time to complete than the previous?
  • Are employees spending excessive amounts of time walking to get product to process? What percent of the time in an operation does a person spend walking or moving?
  • Are the employees spending excessive amounts of time walking to stage product or material to the next operation?
  • Are my work stations close enough to each other? Can I move them closer?
  • Are my employees spending too much time working on equipment?
  • Are my re-makes/rejects too high?
  • What actually is my bottleneck? Can I reduce the time at the bottleneck?
     

Two Plants

Taking these concepts of bottlenecks and line efficiency further, let’s look at two plants producing the same product line, with the same or very similar equipment. The product is an all welded double hung window.
Each plant’s floor is 240 feet by 75 feet or 18,000 square feet. Each one has:

  • 1 frame saw
  • 1 sash saw
  • 1 aluminum cut-off saw
  • 1 miscellaneous parts saw
  • sash and frame fabrication dies
  • 1 two-point sash welder with stacked fixturing
  • 1 two-point frame welder
  • 1 sash corner cleaner
  • 1 sash router
  • and various assembly stations

Plant A is a straight line material flow manufacturing operation with 18 employees (This number excludes screens, insulating glass, material handling, supervision, etc.) producing 70 to 80 windows per eight-hour shift (Fig. 1). The production lines run from one end of the facility to the other with little space remaining for packing, finished goods storage, shipping and staging, etc. This plant uses carts to get material from station to station up to the welder. From the welder to final assembly, components are stacked on the floor beside the processing or assembly station.

There are several things that need to be improved upon in Plant A. Beginning with the frame line:

  • The frame saw is too far away from the fabrication dies. The walk distance to push a cart about 20 feet away is expensive and wastes time. It takes about .012 to .018 minutes to take one step, if an employee walks 500 steps per day, then that would be equal to as much as 9 minutes. Multiply this by 18 employees and that equals 2 hours, 42 minutes that you are paying employees to walk around.
  • The person at frame fabrication probably has about 25 percent of a job and only spends approximately 2 hours a shift punching frame parts.
  • The area between the balance table is used for staging material in carts, thus the distance between fabrication and balance installation creates additional material handling.
  • Each time the balance installer fills a cart or empties a cart he/she (or someone) must move it in order to continue or they must walk farther to get or place material.
  • The frame welder is standing waiting for the machine to process for about 1.50 minutes per frame. Therefore, he/she is actually working (loading/unloading) about 4 hours per day.
  • The space between frame welding and cleaning is used to store material. If the hand cleaning table had been closer, one person may be able to do both jobs.
  • Frame sub-assembly and final assembly should be combined to eliminate double handling.
  • Final assembly is too far away from glazing, but if it were moved down to glazing it would be too far from welding and cleaning.
  • Every station should be balanced to the welder at about a three minute cycle time.

In Plant A’s sash line, there are also numerous changes that should be made:

  • Sash saw is too far from sash fabrication as is the case on the frame line.
  • Sash fabrication is probably less than a full job. It should take about .15 to .20 minutes to process a part. If 6 parts per window are to be punched, this should be only 1.20 minutes worth of work per window. If I can weld two sash in 4 minutes, this means that the fabricator is waiting 2.8 minutes per window.
  • The re-bar station needs to be closer to the fabrication and to the welder to eliminate walking or pushing carts.
  • The sash welder operator is probably spending 2 to 2.50 minutes loading and unloading the welder and 1.50 minutes waiting for the machine to process.
  • Hand cleaning and corner cleaning can probably be done by only one person. The machine cleaner should cycle at about 1.25 to 1.50 minutes per sash including load time (3 minutes maximum per window). If the sash welder is producing two sash in 4 minutes then the machine cleaner has one minute that can be used to hand clean, if necessary. Caution….don’t let this become your bottleneck, or else you could reduce your production capacity.
  • The sash router may be able to be done by the machine cleaner operator, if hand cleaning can be done by the welder. The cycle time of a typical router is approximately .75 minutes per sash or 1.50 minutes per window. Therefore, this person is working 1.50 minutes of every 4 minutes.
  • Sash hardware, taping, and glazing are too far apart. In order for each operator to get material, he or she must walk approximately six to eight steps each way. The same applies to a sash when the operator completes it. Thus each of the three employees is possibly walking as much as 16 steps per sash. That would equal 16 steps x two sash per window x 70 windows per shift x three employees or 6,720 steps total. At .018 minutes per step, that is 121 minutes of walk time for three employees in one shift.
  • Someone must get the sash to final assembly approximately 40 feet away.
     

Other general improvements that could be made to Plant A include:

  • The miscellaneous parts saw is approximately 150 feet from were the parts are actually needed (i.e. glazing bead, sash stops, balance covers, head and sill adapters, etc.).
  • Work-in-process is very high throughout the line. Employees must search for the right component to match the order number or batch number. Work-in-process also causes delays in deliveries since it takes longer for a part to go from the saw operation to final assembly.
  • Orders will get lost easier with high volumes of work-in-process and product will get damaged in house more often.
  • The finished goods area will probably become more congested since very little space is left.
  • Employees on the line will probably pace themselves if their required task takes less time than the one prior or the one after.
     

Plant B is a more compact operation closely resembling a Cellular Manufacturing operation, with 15 employees (Again, this number excludes screens, insulating glass, material handling, supervision, etc.) producing 120+ windows per eight-hour shift.
What is Cellular Manufacturing? Manufacturing that performs as much to the processing of a part of components as possible before transferring it to the next work cell or station in order to reduce material handling costs and maximize work output.
The norm is “I pick up a part, I process it, I put it down.” Then the next persons “picks up the same part, processes it, and puts it down,” and so on, and so on. It sometimes is “I walk to get a part or cart of parts.”
With cellular manufacturing, the concept is “I pick up a part, I process it as much as I possibly can, then I hand it off to the next operation.”
 

In the Plant B layout (Fig. 2), the objective is not to suggest that you layout your plant in this exact manner, but, to offer some ideas that you may want to consider or may apply to your specific operation. Some of the things that improve the operation of Plant B are:

  • The material storage racks have been moved to the area behind the saws allowing space for fork lifts. This also allows us to move the racks directly behind the saws. We also have some racks at an angle along the wall, giving us an additional 34 inches of aisle space.
  • We added a movable weatherstripping station.
  • We move the sash line along the north wall.
  • We created a “mini cell” with the sash saw operator and the re-bar installer to do all of the sash cuts, punching, and re-bar installation. The dies have been placed directly behind the saw fence, so that the saw operator can cut a part and immediately process it before putting it down.
  • Sash bin carts have been removed and replaced with a “pigeon hole” pass-through rack to welding.
  • The welder has been moved closer to the fabrication and within one to two steps to the pigeon hole rack.
  • Minor cleaning duties have been added to the welder operator’s responsibilities during machine cycle times. This amounts to free labor.
  • A pass-through rack is between the welder and corner cleaner, within one to two steps of each.
  • The cleaner operator is also routing sash since we can now balance these duties with the welder. An additional pass-through rack is added for completed sash to go on to the sash hardware station.
  • The hardware station is now modified with support arms to hold multiple sash. It is also set at a good working height. Then another pass-through rack has been added between hardware and sash taping.
  • Consider adding duties from the hardware installer to the sash taping person, such as installing tilt latches, night latches, etc., to keep these two operations in balance. Suspend multiple rolls of glazing tape above the taping table on a bar to keep it out of the way of the taper and to make it readily available when one roll runs out.
  • We angled the glazing operation 45° toward the final assembly area. We added two-tier pass-through racks for top and bottom sash. We set up a top sash glazing station and a bottom sash glazing station.
  • The miscellaneous parts chop saw has been moved so that the glaziers can cut their own glazing beads with only a few steps and the final assemblers can bulk cut sash stops, balance covers, and things like head and sill adapters, slider track, head expanders, etc. Also, the fabrication dies for glazing beads, slider tracks, and adapters have been moved to this area so that parts will not be cut and processed 150 feet away.
  • The frame saw and frame dies are located so that the operator can cut and process all parts. It takes about .40 minutes to cut the average frame part including initial cut and getting material. With four parts per frame, this is 1.6 minutes per window. If I need 3 minutes to weld a frame, then the saw person has an additional 1.4 minutes to process parts in the fabrication dies.
  • We have added a pigeon hole rack to pass parts on to the balance installer.
  • The balance table is within one to two steps of the pigeon hole rack on either side. You want to make sure that the balance installer does not exceed the cycle time of the welder, or else this station may become the bottleneck.
  • The frame welder is also doing some of the hand cleaning shared by a hardware person that is also doing some frame sub-assembly. One cleaning table is shared by both.
  • An A-frame is added to install sash, screens, and miscellaneous parts, and adapters.

The net result of these changes is that work-in-process is reduced throughout the line. Floor space has also been freed up to allow greater finished goods storage. Productivity has increased, cost is reduced, and capacity has increased. Looking at the calculations in Fig. 3, the changes represent $304,457 in potential increased revenue.

Other Steps

Moving completely to cellular manufacturing may be a bigger change than you want to make right now. There are numerous other ideas to consider:

  • Modify die stands so that one die can be placed on top of another to save floor space and travel distances.
  • Don’t make carts, tables, racks too big. It wastes space and increase material handling costs.
  • Use as few batch or order number labels as possible. Try to use pigeon numbers instead.
  • When material or components do have to be moved great distances, then use carts to transport in bulk. Do not have employees taking one or two parts at a time.
  • Maintain your equipment. The lack of maintenance, even simple cleaning or blowing out will cause production inefficiencies, poor quality, and high reject/remakes. Develop a schedule of routine maintenance.

Typically, when manufacturers want to increase production capacity or efficiency, the first thought is “It’s time to purchase new equipment.” In many cases, this is necessary, but there are many other things companies can do to improve their overall manufacturing production and efficiency.

 

Pete Williams is a technical service representative for Chelsea Building Products, a designer and extruder of window, door, and other vinyl building products located in Oakmont, PA. With Chelsea for the past 51/2 years, he has been a certified industrial engineer for the past 20 years. This article is based on plant automation training offered by Williams as a service to Chelsea Building Products’ customers. For more information, he may be contacted at 800/424-3573, ext.258, or e-mailed at pwilliams@cbpmail.com.