What are you paying annually in electricity to run your reflow oven? Not taking into account indirect costs, surcharges, taxes and added wear and tear of running your oven hotter and harder, you might be paying anywhere from $6-8K per line. This number is based off a study conducted at Flextronics Poland, where they pay close to the US national average of $.072 kWh.
Pop Quiz: Can you rank the following in order of impact on lowering your utility bill for your reflow oven?
- Taking Oven Control Measures
- Peak-time Power Up Minimization
- Off-Peak Savings
- Profiling for Energy Savings
Well if you are savvy with your utility bill, you probably identified Peak-time Power up Surcharges as the biggest money drain. You probably did not guess Profiling for Energy Savings as the #2 energy savings technique.
Before I take you through all four techniques, keep in mind there are dozens of variables that come into play. The numbers I use for one municipality and/or manufacturer may be vary by location, but the point should not be lost that you can save money and not sacrifice quality production in the process. As an added bonus many of these techniques may also prolong the life of your oven and have other hidden benefits that may impact your operation.
#1: Peak time Power Up Minimization
The following represents a fairly typical energy ramp up of a reflow oven from a dead cold state. Many manufacturers will use the default start up to quickly get your reflow oven up to temperature and stabilized for production. Thanks to BTU for providing the following data.
Now compare this to an energy savings ramp up mode for the same oven.
By extending your oven warm up time by only ~15 mins, there is a 15 KW difference in the peak energy output. Many municipalities will charge a monthly surcharge based off of whatever happen to be your peak electricity use over typically a 5-15 min period. So if you happen to turn on all your reflow ovens at the same time, AC, coffee machine, PCs, etc., you are in for a big added surcharge on your utility bill that month.
Let’s say you are in South Carolina, Duke Energy charges $13.16 KW as a peak surcharge. Your monthly savings would be $198 per month. Of course if you have more than one oven this savings will be even more significant.
Many smaller manufacturers that perhaps have a single reflow oven, may be close to maxing out on their service. I’ve seen more than one case of a 100 amp facility paying anywhere from $15K – 25K to upgrade to 200 amps. As an example, a 9 zone Heller oven will run at 100 amps at full throttle when heating up, but you can set the oven to heat up in an energy savings mode, knocking your power down to about 63 amps. Suddenly you don’t have to go out and install more service by just making a software change. I know that all the major oven manufacturers that sell to about 80% of the US market (BTU, Heller, Speedline, Vitronics Soltec) have this feature, so check it out.
#2: Profiling for Energy Savings
After 5 years, evidence is pretty conclusive that smart profiling optimization tools can reduce reflow oven energy consumption by as much as 15%. The following three studies demonstrate where power meters were used to measure a “before” profile to an optimized “after” profile, using KIC Navigator-Power or KIC Auto-Focus Power.
- Flextronics – 2004
- Rochester Institute of Technology – 2007
- Global SMT – Delta – 10/2009
There are basically three steps that should not take more than 15 mins to complete:
Step 1: Audit your SMT line speed. You want to determine where is your bottleneck. It is not uncommon to find the reflow oven running faster by 20% or more to the slowest system on your line such as the pick and place or screen printer.
Step 2: Run a profile
Step 3: Run KIC’s power optimization feature in KIC Navigator. As an process engineer I would set up your minimum allowable conveyor speed in the software above your bottleneck speed. For example, if your current line speed is 30 in/min and an audit reveals your screen printer is running at 20 in/min, set your tolerance in the software to 23 inches. You don’t need to make your reflow oven a possible bottleneck! Lastly, you have the freedom to set the maximum allowable process window index (PWI). In other words, if you know your oven can handle using up to 70% of your available spec, without any drift/variability causing you to go at times out of spec, you know your limit. It really depends on the personality of your reflow oven.
Based off the Flextronics Poland study cited above which was conducted on a Heller 1912 EXL manufactured in 2005 and using a kWh rate of $.076 which is practically dead on to the US national average, results in $1062 in annual savings. Which depending on the state of manufacturing can be as high as $2472 annually per oven. 15% savings which was the case at Flex Poland, is not unusual as you will see similar results in the Delta study in Arkansas to be released in October’s issue of Global SMT.
Added features to having KIC’s optimization software Navigator-Power or Auto-Focus-Power are the additional tools you now have for decreasing defects. It is hard for me to know what it costs you each time you send a PCB to rework, the cost of time spent profiling when you should be making on-time deliveries and the stress and aggravation of trying to produce a run of a 100 boards when your customer wants all 100 back! Auto-Focus power allows you to make a very good first guess profile of new board before you even profile! You can find discussions on these tools throughout this blog.
Off-peak hours vary widely per locale. Also depending on the time of year it can vary. Nevertheless, if it is possible to run even a portion of reflow production in off-peak hours your costs kWh can sometimes be half of on-peak prices. I like to use the same rate chart example give above for S. Carolina where Duke Energy charges between 2pm – 6 am, $.0297 kWh vs. $.0563 kWh. Many of us logistically may not have in place a night shift, but most of us can certaintly take advantage of production after 2pm. This is more an issue of smart planning, an exercise in management.
If you can schedule a quarter of your production off-peak, and by doing so are able to reduce your rate per kWh by half which is possible in some municipalities your savings could be on the order of $62-74 per month per reflow oven. I came up with this number by again using the Flextronics study as a guide, where they are paying a kWh rate similar to the US national average and shelling out between $5.8K – 7K per year per reflow oven.
#4: Oven Control Measures
By buddy Bob Powledge of DG Marketing out of San Antonio, Texas likes to say, “sure the heck cheaper to blow air than to heat it up!” I agree and there are studies to prove it. Basic physics comes into play. It you can move more heated air over a surface, it will heat up more efficiently and faster. This is why squirrel cages have by and large gotten bigger over the years and other technologies such as static pressure have come about. In one study conducted by BTU who plays around with the idea of static pressure another approach at improving heat transfer rates, the same set-points could increase temperatures by as much as 5C by only changing static pressure. Take this to the next step in our discussion, you can thus REDUCE your oven set-points by that same amount thus reducing electricity usage. Just a word of caution. If you use blowers, you don’t want to crank them up too much unless you like moving components across your PCBs. Many ovens have precision controls for this reason while others offer this as an add on option.
I have to take a wild guess in what this translates into dollars since there has not been a study specifically addressing what this means in terms of electricity savings. Considering we have so far been able to build cost models from the profiling studies we can extrapolate some reasonable numbers. In the Delta study, the cumulative setpoint change across their 8 zone Vitronics Soltec oven was 198 C. If you run through each zone, some zones like Z1 there was no change, but when you get to Z5 the delta was 50C! So how do you compare both? If you achieve a 5C reduction across 8 zones or cummulatively 40C and you compare this to our 198C study, this would represent 20% difference. So take our numbers from our profiling study and cut them down to 20%. Remember in the national average example, you could expect $88 in mountly savings per reflow oven, therefore for this example we might see about 20% of that number or $17 per month per reflow oven. I please welcome any oven manufacturer to share the results of a study that questions these assumptions since some guesswork is involved.