Wood component makers commit to yield improvement.

Results of a new survey of rough mills reveals a heightened use of optimization technologies and strategies.

The Wood Component Manufacturers Assn. (WCMA) decided to embark on an aggressive campaign in the fall of 1994 to help its members identify strategies for improving lumber yield.

In the first phase of this consolidated effort, the U.S. Forest Service's Princeton Lab conducted rough mill yield simulations for several WCMA companies in order to derive estimates of optimal yields for the types of cutting bills and grade mixes processed by wood component manufacturers. These estimates can serve as target yields for crosscut-first and rip-first operations. These results were included in the 1995 Dimension Purchasing Guide published by Wood & Wood Products last June (Wiedenbeck and Thomas 1995).

The current focus of the yield improvement campaign is to identify yield performance ranges based on actual production statistics then correlate the yield data with information on rough mill practices to establish how different operational factors impact yield. A WCMA survey conducted in March/April 1996 provided a wealth of information for this phase of the yield campaign. Survey respondents provided information not only on their mill's yield performance, but also on their equipment, their operational practices, their modernization plans, and current trends impacting the wood component industry.

Key considerations for rough mill improvement: Observations and survey results

With so many factors impacting yield, how can you begin to know where you should focus the efforts of your yield improvement program? Today, the most common response to low yield and reduced profit margins seems to be to invest in new optimizing equipment. This response makes sense if you know you have fine-tuned your existing system so that the incremental improvements you might still squeeze from it won't compare with the yield gains you can expect from the optimizing saw or fingerjointer that is on your wish list. But do you know this to be the case?

It is difficult to recognize when you are nearing the full yield potential of your current system if you lack a focused rough mill yield improvement program. A focused yield improvement program should have at least one person whose job responsibilities are dedicated to yield improvement. The "yield coordinator" can explore the yield potential of different processing and equipment strategies by conducting tests in the rough mill and by running yield studies on the computer. Only if you know the yield statistics for your different pieces of equipment, different grade mixes and different cutting bills can you possibly know the relative merits of different yield improvement efforts.

The remainder of this article reviews and comments on some of the results of the 1996 Yield Practices and Performance Survey encompassing 38 members of the WCMA.

Survey results: Fifty percent of the 38 WCMA members responding to the survey indicated they have a yield coordinator at their miIl. Forty-two percent of the 38 milIs use yield simulation computer programs for rough mill analysis.

Comment: You can explore the relative yield benefits of different processing strategies, equipment types, lumber grade and size mixes and product lines using the Forest Service's gang-rip-first rough mill simulator, ROMI-RIP (Thomas 1995). Over 300 copies of ROMI-RIP have been put into use by the industry since the program became available in the summer of 1995. Get your free copy of the program by contacting Ed Thomas of the Princeton Forestry Sciences Lab at [phone].

Survey results: WCMA members were asked what equipment or processing strategy changes they had made during the last two years in an effort to improve yield. The five most frequently cited changes were: 1) purchase of an optimizing chopsaw, 2) purchase of a finger-jointer, 3) purchase of an optimizing gang ripsaw, 4) purchase of an optimizing crosscut saw and 5) implementation of new lumber grade or quality specifications.

Comment: Do you know if the piece of equipment that you want to buy can be optimally utilized in your system? For instance, many of the yield benefits to be gained from installation of an optimizing crosscut or chopsaw relate to the ability of the saw's optimization program to efficiently handle additional part lengths and grades more readily than can a human operating the saw.

We recently completed a case study looking at the yield benefits of cutting more lengths at a time on the chopsaw. We found that by combining orders so that 15 lengths are set up on the chopsaw at one time versus cutting the same 15 lengths with only five lengths on the saw at one time you can pick up approximately six yield points. Yet, it is not uncommon to visit a mill where optimizing saw(s) have been installed but part sorting capacity still imposes a limit on the number of part sizes and grades that can be cut at one time.

Survey results: Fifteen of 37 (41%) WCMA members responding to the 1996 Yield Practices and Performance Survey operate one or more optimizing crosscut or chopsaws. The number of lengths put on the saw at one time typically ranges from four to 17 with eight lengths being the most common. Only 11 of 37 companies cut three or more part grades at a time.

Comment: When evaluating your rough mill automation options, gathering information from machine manufacturers is an important step in the process. But how do you sort out the differences between similar machines made by different companies then decide which equipment options will be of greatest benefit to your operation? You can find answers to many of your optimization equipment questions in a comprehensive publication on crosscutting/chopping systems. The information in this publication was researched and compiled by various people, especially Nick Weidhaas and Ed Jerger at North Carolina State University, and it is available from BC Wood Specialties (North Carolina State University 1996). This publication, in combination with ROMI-RIP simulations, can help you distinguish those machinery features that will be most beneficial.

Another classic example of a new technology that has been widely adopted but often is grossly underutilized is the optimizing gang-ripsaw. Many mills have added gang-ripping capabilities to their existing crosscut-first rough mill creating a dual system that offers incredible processing flexibility and yield opportunities. Yet, most mills added their gang-ripsaw lines without adding additional lumber sorting capacity that would enable them to send boards to one line or the other depending on board quality and size characteristics.

Survey results: Thirteen of 38 (34%) WCMA members responding to the 1996 Yield Practices and Performance Survey have a dual system (both rip- and cross-cut-first capabilities) in their rough mill; 20 of the 38 respondents have a strictly rip-first system and only four of 38 have a strictly crosscut-first system. Sixty-one percent of the companies using gang-rip-saws have fixed arbor saws. ([ILLUSTRATION FOR FIGURE 1 OMITTED], page 206.)

Twenty-four of 35 (69%) WCMA members responding to the question "Do you try to match cutting requirements with available lumber supply to best utilize the lumber you have available in dry storage?" indicated they always try to match inputs with cutting requirements. Eighty-two percent of those who do some lumber presorting match lumber grade with cutting requirements, 68% match lumber length, and 37% match lumber width.

Comment: Yield results point to remarkable yield gains that can be obtained by matching lumber inputs with cutting needs (Gatchell et al. 1996). These same studies and many others highlight important lumber preprocessing strategies that can lead to significant improvements in rough mill yield. Charlie Gatchell of the Forest Service in Princeton, WV, identified the importance of cutting out crook in gang-rip-first processing in a series of studies that he completed earlier this decade (Gatchell 1991). Finally, this last couple of years we have seen crosscut saws being designed into many new gang-rip-first systems to do exactly what Gatchell has advocated.

Survey results: Ten of 33 (30%) WCMA members with gang-ripsaws who responded to the 1996 Yield Practices and Performance Survey indicated they have a crosscut saw positioned in front of their gang-ripsaw for cutting out crook. Seven of these 10 respondents indicated their rule-of-thumb was to crosscut boards having crook equal to or greater than 1 inch.

Comment: It may not be replacement of outdated machinery or automation of the simplistic manual operations that offers the greatest yield gains. In fact, it may be that your greatest yield gains can be derived from efforts targeted at parts of the business that you may not typically think you have much influence over.

For example, consider what you might do on the lumber supply end of your business to get more useable wood and perhaps ease lumber prices at the same time. Can you work with suppliers to establish lumber specifications that are better suited for your processing system and product? This might include helping your lumber suppliers learn how to edge and trim lumber less severely so you can obtain more useable wood. It might include accepting shorter lumber from suppliers providing it meets certain clear-area specifications and is stacked in single-length stacks.

Optimal lumber grade mix is one raw material factor that most companies have spent time addressing. Optimal grade mix depends on both product and processing system. A key factor to consider when evaluating the adoption of new equipment has to be how the optimal grade mix might change when the new equipment is installed. Will an optimization system allow you to reduce your lumber grade mix without impacting your yield or your ability to meet orders? Perhaps, instead, you will need to raise your grade mix to keep the optimizing saw fully utilized in order to fulfill your return on investment expectations for the investment.

How might the introduction of an optimizing saw impact throughput and bottlenecks? We have observed that optimizing crosscut/chopsaws are frequently bottlenecked at the marker station. When the markers are rushed, they may make suboptimal decisions that hurt yield and/or lead to higher reject rates downstream. Some mills respond to this bottleneck problem by upping their grade mix so the markers can process lumber/strips more quickly. Is the net result of this "optimization" effort really cost-effective? This is why it makes good sense to visit other mills and seek advice from a rough mill specialist if you are considering the adoption of a technology with which your company has little or no experience.

Survey results: On average, the grade mix distribution of the 38 WCMA members who participated in the 1996 Yield Practices and Performance Survey was: 10% FAS, 15% F1F or Selects, 48% No. 1 Common, 25% No. 2A Common, and 2% No. 3A Common (and other grades).

The average yield (based on dry lumber volume) for the 37 companies that provided yield data was 62%. Individual yields ranged from 45% to 88%. Grade mix alone did not contribute substantially to an explanation of yield differences between mills. ([ILLUSTRATION FOR FIGURE 2 OMITTED], page 206.)

Comment: When we speak about yield and how simulation can be used to help answer important operational "what-ifs," we always cite three major areas that influence yield: raw material, processing and product. Just as there are opportunities for wood component manufacturers to work on the raw material end of the spectrum with lumber suppliers to promote relationships that can lead to improved wood utilization, there also exist significant opportunities on the product end of the spectrum. These opportunities range from the routine, such as finding consistent customers for shorts and edge-glued panels, to the more innovative, such as working with others to promote expanded market opportunities for finger-jointed dimension, character-marked parts and dimension that is more variable in color.

Survey results: The major product categories for the 38 responding WCMA companies were: 1) edge-glued panels (21 companies), 2) cabinet parts (19 companies), 3) mouldings (19 companies) and 4) cut-to-size blanks (18 companies).

On average, 52% of the cuttings produced by the respondents were clear-two-face quality, 34% were clear-one-face, 4% were sound-interior and 7% were character-marked exposed. On average, 55% of the parts produced by survey respondents must meet market-imposed color restrictions.

According to the 38 WCMA members who responded to the 1996 Yield Practices and Performance Survey, the five most important industry trends impacting yield are: 1) scanning, 2) optimization, 3) demands for color matching, 4) acceptance of fingerjointing and 5) acceptance of character in dimension parts.

Only 11 of the 38 (29%) component manufacturers who participated in the 1996 Yield Practices and Performance Survey are fingerjointing. Those that do fingerjoint estimate that fingerjointing has increased their rough mill yield by 6%.

Comment: The WCMA is an active organization supporting collaborations and research that foster improved wood utilization. WCMA members demonstrated their commitment to improved yield in rough mill operations when they responded so strongly to what was a quite lengthy and demanding survey (reported on in this article). We look forward to delving further into the information we gained in this survey to better establish the relationship between rough mill yield and important yield factors such as the lumber grade index, the cutting size index, the cutting quality index and the technology index.

For more information, contact the Forestry Sciences Laboratory, Attn.: Jan Wiedenbeck, 241 Mercer Springs Road, Princeton, WV 24740; [phone] or FAX [phone].