STEEL SAFE

Posted on December 4, 2022 by george

Machining fixtures use datums to locate castings

We are all aware that welded surfaces on high pressure casting die inserts prematurely heat check. Heat check is not something that we want on machining datum surfaces. In the pictured transfer case casting the part rests on three ears in the machining fixture. I have colored the datum surface on one ear red. The dimensional accuracy of this surface will determine whether sufficient machining stock is provided on the rest of the casting.

One of the most effective methods of reducing exposed porosity is to reduce machining stock thickness. This is because the skin of a high pressure aluminum die casting is porosity free due to rapid solidification. As we reduce the provided stock thickness shrinkage and warp of the casting becomes a factor in reliably achieving machining clean up

Skilled die cast shops have discovered that a more accurate casting shape can be achieved if the die shape is biased to correct for warp. This is accomplished by adjusting the die shape using a first sample casting. Certain area on the mold are initially created with ..25 mm extra mold steel. This is where we get the term “steel safe” The pictured datum surface is a prime example. It is unacceptable to bias a mold shape to compensate for warp by welding datum surfaces. Adding extra steel makes weld free correction possible.

Residual Stress

Posted on July 10, 2022 by george

Tempered glass used in automotive windows shatters into small pieces. This is due to the residual stress in the material. The two surfaces are in compression. The interior is in tension. Many cut injuries have been avoided because of this choice of material.

Die castings also have similar residual stress. No, die castings do not shatter into 1000 pieces but they do warp when only one surface is machined off. This makes it difficult to machine a die casting to a precision dimension. As a further challenge the part does not immediately relax into its final warped shape. I have fought with parts that were still warping a day later.

So what can you do to compensate for the residual stress in most die castings.

Heat treat- Not a popular option because many die casting blister in heat treat
Bias the machining- With modern CNC it is possible to shape a cut to obtain the desired final shape after warp
Cut more than once- A roughing cut followed by a finishing cut after a time delay is commonly used to achieve round bores. The pictured rear seal retainer required 30 roughing cuts.
Machine off less material- My favorite solution but it does require a lot more die cast engineering skill
Machine unclamped- A process like Blanchard Grinding where a part like an oil pan is nested instead of clamped allows the part to relax the residual stresses as it is being cut. It is possible to achieve a .06 mm flatness on a engine block mating flange because the Blanchard grinding process also uses multiple cutting passes

Counter Bore

Posted on July 11, 2021 by george

The old addage “If the only tool you have is a hammer, every problem is a nail” Eliminating sharp edges fit into the same category “if the only tool you have is a chamfer ever corner is at a 45 angle” Imposing a one size fits all solution to a problem creates sub optimum results. This discussion is about adding counter bores to your design arsenal.

Machined 45 degree chamfers work very well when both adjacent surfaces are machined. In the picture you see a yellow 45 chamfer on the corner from the mounting surface to the bore. This was machined into the plates. On the opposite end of the bore a counter bore replaced the chamfer. This counter bore is on the corner between a unmachined face and the bore. The counter bore was created by interpolating the bore roughing cutter. This resulted in a uninterrupted cut by the fragile finish bore cutter which solved a cutter chipping problem,

Cast counter bore are used when a machined surface connect to a cast chamfer. The counter bore solve the tolerance issue and insures that the chamfer diameter is never oversize.

Front Load

Posted on February 27, 2021 by george

Core pins are normally used to solve the short life expectancy associated with near net cores. A good example is a starter nose casting. Because starters are high volume and unchanged from year to year they are very low cost margin products. Core pins create features such as chamfers that would normally be machined to achieve the required manufacturing cost. Very little wear can be tolerated on a core that is creating a feature that otherwise would be machined. This explains the short core life.

On many larger parts it is possible to incorporate holes for traditional core pins without encroaching into the thermal passages. On a part like a starter nose adding traditional cores messes up the die cooling on the ejector side of the die. I even worked for a guy who tried building a die for this part without cores. Front load cores can be installed on top of the thermal passages. In addition to solving the cooling issues it became possible to renew a broken core without pulling the die from the machine. This is very effective when you approach core renewal as a preventative maintenance activity replacing cores before they break.

Dot to Dot

Posted on October 16, 2016 by george

We all learned to create
pictures by connecting the dots.

A simple child’s task like connecting the dots matches a computer’s capability. This was especially true in the early days when computer numeric controls had a lot less intelligence. It was a stretch for the computer to perform a simple 2 dimensional connect the dot task. Even todays CNC (Computer Numerical Control) is based on connecting dots with straight lines.
We began the computer controlled manufacturing revolution by using simple 2 dimensional dot to dot. In the very beginning there were long distances between the dots. The parts that were CNC manufactured had facets like you see on diamonds. As Moore’s law has given us more computer memory and horsepower we use ever greater numbers of dots to the point where the facets caused by straight line connecting of the dots are perceived as a smooth blend. A simple 2 dimensional approximation of a circle using a ring of dots connected by straight lines has evolved into a the chain of connected dots that has lengthened to stretch many miles.

A string of connected dots, many miles in length guides the path of a cutter used to make a mold

As we acquired more computer horsepower we wanted to expand into three dimensional objects. We again looked for the simplest way. A straight line connecting two dots was evolved into a set of three dots connected by straight lines defining a plane in three dimensions. Computer defined three dimensional objects look a lot like geodesic domes

Tyranny of numbers came to get us. Whereas we were able to manually program CNC machining G-code and moon landings by creating the travel path dot by dot, it simply was not humanly possible to define all of the little triangles needed to define an object shape. The STL (STereoLithography) data format we created for the task actually is capable of defining just about any shape that we can conceive. It was the early 90’s before any version of CAM (Computer Aided Manufacturing) software could generate a complete enough STL shape definition to be commercially useful. It was the turn of the century before any CAD (Computer Aided Drafting) software caught up to the same level. The underlying issue is that most of the part shapes that we use are not pure cubes,cylinders or spheres. In the classic example, three different radii meet at a corner. What is the shape at the corner? Turns out the computer does not know either.

The historic solution to the three different radii meeting at corner, was to instruct the pattern maker to do a blend. The digital solution started out in a very similar fashion. The STL file was manually adjusted by a person. This time consuming and costly step is one of the impediments slowing the adoption of 3D printing. The incredibly slow 3D printing speed is fast compared to the time need to clean a STL data file triangle by triangle. Moore’s Law keeps advancing. Each generation of software and 3D printing hardware opens the door for new affordable uses. Even though 3D printing theoretically has the ability to create any shape, in the near term it will have economically imposed shape limitations like any other manufacturing process

Lights Out Manufactuing

Posted on June 10, 2016 by george

It is hard to imagine a life before we used electric lights

The introduction of bright plant lights made 3 shift operations possible. Sufficiently bright lighting is interpreted by the workers internal clocks as sunlight. In most 24 hour settings it is important that the off shift workers are alert and attentive. This is only possible if their internal systems think that it is time to be awake. You would not want everyone to be asleep if you arrive at the hospital emergency room at 3:00 am.
Times when we are without lights turn into events in our lives. I can still remember one evening when we were having a boxed murder mystery party with friends. In the middle of the game our house lights went out. This looked suspicious because of a lack of bad weather and the neighbors houses with lights on that were visible through our windows. ” OK, How did you do it?” My friends know that I am an engineer.

Even though I was the murderer in our game, the loss of lights was the local utility company transformer giving up the ghost.
Lights out manufacturing is one of those “overnight” revolutions that have been in the works for more than 20 years. In the 90’s there were very few pieces of manufacturing equipment that you could trust to run overnight unattended. Electrical Discharge Machining (EDM) was one of the first manufacturing processes to be used in a lights out fashion. Yes, we did need to add automatic halon fire extinguishers just in case.

The highest precision manufacturing processes like EDM occur at slow speeds

This process is heavily used in mold making. It was a natural for unattended operation because some of the cuts can take days to accomplish. Many mold shops run their expensive EDM machines unattended overnight and over the weekend.
Lights out manufacturing has emerged from the bowels of tool and die manufacturing. A couple factors are responsible because implementing lights out manufacturing is not as simple as running over to the electrical breaker panel and snapping off the lights. ( Usually chaos ensues when the lights fail while people are working.) First our control systems are more reliable. Second, we can include more sensors to handle adjustment or shutdown if we are not present. Third we have adopted more slow speed manufacturing processes like 3D printing which take long periods to accomplish.

Photo courtesy of i.materialize.com

A good modern example of lights out manufacturing is the Amazon (Kiva) robots that happily operate in a dark warehouse because they are part of a system that was initially set up to operate in that fashion. Welding robots are another good example because they have the sophisitcated controls the enable then to run unattended. Welding robots can finish the job they are on after everyone goes home because of proper engineering design.

Sophisticated computer controls allow welding robots to run unattended

Laser and water jet cutting machines for sheet material can operate in a lights out manufacturing environment. The usually means that the jobs are packaged into full sheet set-ups so that sufficient time is gained by finishing jobs after everyone goes home.
We all remember the fairy tales of our youth where the elves came and did our work while we slept. It is more than a fairy tale. I still find it amazing seeing the progress that occurred while I slept when I arrive at work in the morning. Manufacturing will come back to North America. Some of it will come back as lights off manufacturing. Innovators in the manufacturing space have discovered that it is necessary to implement the latest manufacturing techniques and equipment to make a profit at an attractive selling price.

Change

Posted on November 15, 2015 by george

Historic 2 man saws no longer match the OSB wood we build with today

My grandfather was a carpenter. In the Finnish community, this was a common profession. Finland is a land of many trees. Many of the immigrants arrived with the practiced skills and tools for working in wood. As a tiny boy, I was fascinated by the two man saws, augers, planes, chisels, files that were used in the craft. I inherited the Audels manuals that taught the methods for building a structure without using any nails. Sharpening was a key skill. Many hours are needed to file and set each tooth on a saw so that it cuts straight and true. This insight transferred into my occupation in custom metal cutting cutter design. The tools themselves are no longer relevant. A two man saw used to cut planks from timbers is not appropriate for cutting 4×8 (In true change fashion now a slightly different metric size) sheets of OSB (Oriented Strand Board). In a earlier age, ancient northern trees were cut down. The trunks were cut into timbers and floated back to civilization. The rest of the tree was left to decompose. As human population grows, it has become necessary to utilize more of the raw materials. Pretty much all of the wood of a tree can be shaved into the flakes that create OSB board. The sharpening skills of craftsmen have been replaced by mass produced cutting edges made from high technology materials.

All gas stations used to be full serve

My first job was pumping gas. This was consistent with my auto mechanic training and automotive design career goals. Not too bad in the summer. Out in open when the weather was bad. Checking fluids was necessity for most patrons. More reliable cars and self serve made all of that go away. A roof over the pumps made the task palatable for the general public. One of the interesting features of change is that old methods come back with a twist. As we adopt driver-less trucks, the gas pump jockey will reappear. Instead of fill the Truck with diesel, the fuel will be liquefied natural gas. Methane has 4 hydrogen atoms instead of 2 per carbon atom in diesel fuel. We need to make a dent in carbon and black soot emissions.
There won’t be quite as many trucks on the road though. Trains are more fuel efficient at moving goods. I suspect that the gentler grades are a big factor. The autonomous technology that guides AGV (Automatic Guided Vehicles) around warehouses will dispatch a myriad of driver-less train cars to the individual train sidings that lie unused around the country. Again this will come back with a twist. The size of the train car will be adjusted to match the sea land container that now dominates the transport of goods. The receiving plants will invest in the track fans needed to directly unload the cargo in the same fashion that multiple truck docks are currently implemented. As is true in most transitions, we will see loading docks with train rails that can also serve as truck docks.

Loading docks can serve either trucks or properly configured autonomous rail cars

In much the same fashion that the ocean shipping converted from bulk cargo to containers, this change will migrate into the rail industry. As always change happens with a twist.

Format Wars

Posted on November 1, 2015 by george

The VHS vrs Beta war raged for many years

The VHS verses Beta cassette tape war is the classic example of a format war. Consumers who purchased a video tape player desired to purchase every future tape in the same format. Once they had a collection of tapes, even wearing out a tape player was not going to get them to change. The furniture industry jumped onto the bandwagon making shelving units to house our collections of tapes. This war raged on without a winner or loser until the DVD splashed onto the scene.

The small size of the DVD
media displaced our use of Video tapes in a few years

. In the near future high speed internet and streaming video will displace DVD as the pace of technology accelerates. Streaming video will cause us to forget about the blue ray format war that superseded the Beta / VHS battle
Some format wars last for many years with no end in sight. A good example is the metric system. The engineering community had no problem quickly adopting metric dimensioning on drawings. In CAD especially, converting from one dimension system to the other is just a button click. The problem arose with legacy thread pitches. In the beginning of the industrial revolution, the first lathes were set up to create threads. In Europe these lathes had metric sizes. As luck would have it the imperial fine and coarse threads turned out to have better properties than fine and coarse metric threads. A rusted imperial coarse thread bolt can be loosened while a metric bolt usually must by drilled out. A imperial fine thread bolt will break unlike an overtorqued metric fine thread bolt that strips before it breaks.

Metric fine threads are prone to stripping

The imperial fine thread was invented by the Society of Automotive Engineers and is also called a SAE thread. They were looking for a thread that would not vibrate loose. A metric coarse thread is half way between a imperial fine and coarse thread. If it is perfectly tightened it will not vibrate loose. (US car mechanics had to purchase torque wrenches when metric bolts were adopted.) Most molds manufactured anywhere in the world use imperial coarse thread bolts. Companies cannot afford the expense of drilling fasteners every time they need to disassemble molds. The world conversion to metric is pretty much complete. It is possible that threads may be like pipe sizes. The world may continue to use the legacy imperial threads and pipe simply because they work better and the matching taps, fixtures, and related manufacturing equipment are already in place.

In the early days, when Microsoft was trying to displace Lotus, Timeline, Word Prefect, etc. they focused on interoperability. Once they became the dominate player they elected to create new file formats for Excel that could not be imported into Open Office. This may have worked for them if they had taken the time to verify that their newest version could successfully import legacy data. Companies which invested thousands of manhours in creating Excel files chose to continue to use the earlier version when the new release could not preserve the formatting. It is possible that Calc in Open office will never bother to write the code for importing the latest version of Excel. As a small fish caught in the turbulent format war water, my http://mileagetrakker.com application creates reports in the Excel 97 format.

Nail down your mileage deduction

Our users want compatibility. It does not matter whether they are using either version of Excel or Open Office Calc. The 97 format can transfer into any of them.

Visual Management

Posted on October 25, 2015 by george

Our eyes are heavily linked to the thought
processes of our brains

Seeing is believing. We rely heavily on sight to guide our actions. Accordingly, seeing something for ourselves is a powerful way of having us believe it. When we plan systems to control manufacturing activity, the ones that use things that we can see to guide our decisions work the best. This week I was attempting to solve an accuracy deficiency on a high RPM vertical CNC machining center. This machine is used to cut graphite to make EDM electrodes for mold making. The CAD/CAM cutter path software guided shapes, cut using diamond tipped tools, need to be accurate to better than 0.001 inch (0.04mm) on all surfaces. This shape accuracy is needed to obtain the taper needed to eject parts from the mold. 0.001 inch is a tiny distance that is difficult to see and measure. A experimental method that I call a 6 time repeat study is very effective adding visibility to the task. In this case, we machined a test shape using the CNC. After the graphite was cut we used a yellow paint marker to color all surfaces that were machined. The exact same cutting program was run again. Low and behold, one face showed uncut and completely yellow.

A painted test block shows the backlash in the X CNC axis

My machinist could not understand why I called the test a 6 time repeat study. We had only run the program twice. I indicated that once the machine flunks it is no longer necessary to run the remaining passes. Had the part been black on all sides after the first rerun we would have run the program five more times painting in between every cut to confirm that the machine consistently cuts accurately. I had originally thought that my problem was a worn spindle bearing due to the 15000 RPM cut. The actual test part only has a hint of the zebra stripe that a worn spindle bearing creates. The 6 time repeat test for metal cutting CNC machines is similar. I machine a precision bore as the test. A black Sharpy is used for coloring the bored hole between each repeat.

Segeo Shingo correctly taught that every manufacturing operation needs to leave a visual indication that it has been begun. He was careful to distinguish visually confirming that an operation has been begun from inspecting that it has been properly performed. His experience matches mine. For every part that is made with an operation that has been improperly performed, 9 parts are made with that same operation missed. A good example is a rough boring operation. After the part is finished machined there is no way to visually tell that the roughing bore (or drill) actually happened. A missed rough bore is a problem because the only way to achieve the desired roundness in a precision bore is to set the rough cut size so that it only leaves 0.010 inch (.4 mm) stock for the final cut. I am happy to report that the advent of CNC machining centers gives us a few more options. One of my favorite tools is to use a helix orbit to add a counter bore. I make this cut using the roughing cutter after it finishes its bore so that I can either gage or visually confirm that the cutter has not chipped. (In the pictured example, the helixed counterbore using the robust roughing cutters also protected the fragile finishing cutter from the weld located at the start of the bore.)

Adding a CNC helixed counter bore made by the roughing tool makes visually confirmation possible

Adding a CNC helixed counter bore made by the roughing tool makes visual confirmation possible

A classic example of a manufacturing operation that leaves no visual witness is bolt torquing. This becomes a problem when multiple bolts are needed to secure the joint. On a excavator, the turret is secured with 24 to 36 bolts depending on size. If one of these bolts is not tight, the operation of the unit will work it loose and zipper apart the entire joint. The repair, in one years time, is a $20,000 warranty cost. Confirmation of proper bolt torquing is further complicated by the locktite used to seal rust out of the thread. Checking bolt torque a day later only confirms that the locktite is working. This is where Shingo’s visual management concept fits in. Every operation needs to leave a visual witness that it has occurred. This warranty cost was eliminated by redesigning the bolt tightening wrench so that it left a mark when it was used to tighten a bolt. It became possible to visually see walking by that every bolt was tightened.

Final torque wrenches should leave a visual mark when they are used

Not every application can tolerate a scratch in the paint. I have also modified open end wrenches and sockets so that they leave an imprint on the bolt head or nut when the torquing operation is performed.

Feedback

Posted on September 27, 2015 by george

It is easier to hit the target when you employ feedback

When I first embarked on a campaign to knock seconds out of my CNC cycle times, a few eyebrows were raised. The doubters lacked the experience to realize that just about every quality deficiency or design change would add task steps and cutting time to the CNC cycle. Multi million dollar CNC machining centers usually do not have spare capacity. The direct feed back made this a good starting Kaizen project to tackle with my machining team. Our successful effort was just in time to support the next generation of models which included additional machined features. Next on the Kaizen plate was an attack on cutting tool usage. Even though we utilized the excellent feedback loop of a run chart, the actual life of the cutting edge was poor. Fortunately introduction of TiALN coating of the carbide inserts eliminated the size drift of the bored hole.

Surface technology advances dramatically increase cutter life

We were happy about the resultant $250,000 annual reduction in cutting tool purchases and the saving in down time related to cutting edge replacement, but we lost our run chart feedback loop. The cutter held bore size until it chipped. We needed a new feed back loop. In the short term we switched to 100% guaging of every part. When an edge chipped we replaced, reset and rebored before removal of the part from the fixture. This proved cumbersome. Our team wanted to automate measurement using the CNC and the probe. Combo cutters were designed and purchased to knock more seconds out of the cycles. We had switched to through spindle oil mist lubricant to save part washing and smell. More feedback required. An artifact was added to the fixture with a reference bore size so that the probe could be calibrated to measure the part at the current ambient temperature. We had lost the temperature stability that comes with flood coolant. We discovered that it was not enough to detect the wear of the finishing cutter. A chipped roughing cutter also spoiled the bore roundness. This is especially true when it is also necessary to cut through weld. Using good visual management feedback practice the roughing cutter was helix orbitted to replace the lead in chamfer with a counterbore.

Counterbores made using the rougher enable visual management of cutter chipping

Finally we closed the loop. The probed rough and finish diameter measurement presented the correct tool for cutting edge swap immediately upon encountering a worn insert. Modern machined accuracy is always the result of properly planned feedback

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