Engineering a Solution. A high speed drill application: Introduction:

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1 Engineering a Solution. A high speed drill application: Introduction: Here at Motion Technologies, our motto is simple: There is no such thing as a problem, just that a solution has not been found. This is quite a bold motto to live by, though we have experience in all forms of linear and rotary motion to find the solution. I am quite proud of the depth of knowledge that Motion Technologies currently has. This combined with 30 years of doing the too hard jobs makes it easy! We have the knowledge, and this instills confidence with our customers as we quantify on request, or for want of better word, warrant the engineered solution. This white paper describes a customer problem that Motion Technologies engineered a solution for. Of course there is many ways of engineering a solution, and in this application you can see the different solutions that were presented which organically grew to an outcome that the customer wanted to purchase. I hope you enjoy the read and gain some knowledge along the way. Regards Paul Mccleary, General Manager of Motion Technologies. System problem: Motion Technologies Solution Engineer Mark came across a customer problem which required the drilling of 4 holes in a train coal car. This may sound simple, however the holes were 24mm diameter and had to drill through 32mm thickness in high tensile steel. The holes had to be drilled with an accuracy of 0.1mm. This does not sound very complicated, but when you have to drill upside down it is near impossible to meet the accuracy between holes. This customer had in excess of holes to drill. At the time the customer s workers were planning on using magnetic drills and the coal car was to be lifted with a crane to make access simpler. A customer budget was requested and advised. This is very important as money does cure all ills as they say. The base parameters for the project were as follows: Automated drilling. Fast drilling Accuracy of holes and hole centers Simple to operate. Operating outdoors. 240 volt 15 amp 1

2 Engineering Design: A decision needed to be made on what type of drill to use. We did consider using a magnetic drill and modifying it to the application, though this had 2 major problems. The IP rating being out in the weather would cause short life cycle of the drilling machine and secondly the internal lubrication system of this type of drill, is not designed to be operated upside down. Thus the grease inside the gearbox of the drill would run into the motor. Additionally a decision needed to be made about the drilling machine and drill bits. The decision was to make a drilling machine designed for the environmental conditions. Next was the actual drill bit. Twist drills required a lot of force without a pilot hole and the torque required to turn the twist type drill was very high. Based on the amount of power required, we were to exceed the 240v 15amp power. A final decision was made on a hole saw from Germany that had 3 cutting edges and 3 cleaning edges to remove the swarf from the cutting area. At Motion Technologies we make a spreadsheet with formulas so as to work different scenarios. The above Drilling calculator spreadsheet is an example of running numbers. This sheet was generated in order to work out torque requirement of drill spindle against different gearbox reductions. Once we knew the spindle torque we could then size the gearbox and motor combination. The eventual outcome was 0.35kW motor, 7.5:1 gearbox, Spindle speed of 400 rpm and 0.15mm per rev. 31 sec is what was calculated to drill through 32mm steel. Power required 3.6amps 2

3 Next decision was how to place this drill in 4 positions. There are many ways we could have moved the drill into positions required, including linear X and Y axis with pre programed moves, though due to robustness we decided to use a drive slew ring, which we would use a servomotor on. These drive slew rings can take massive overturning moments Think of a crane where the cab and gantry rotates. What this did was allow positioning of the drill to pre programed positions with 1 servomotor. Using a conventional X and Y axis table required 2 servomotors, programming associated with it, and mounting difficulties. The below is the most extreme drill you have ever seen. The picture on the left is a side elevation of the drill. This concept required utilizing a screw jack as the drill. A screw jack in normal life is designed to translate a screw for lifting or holding weight. The screw jack has an input shaft that can be motor driven to make the translated move. At the end of the screw bottom is a motor and gearbox combination rotating the screw and has anti rotation using a linear rail. How it works; the motor at the bottom provides the speed of the spindle and the screw jack is backward driven by another motor to control feed rate. Did I mention at the beginning that Motion Technologies does think outside the square? The picture to the right above is a plan elevation, utilizing the drive slew ring I mentioned earlier, which rotates the screw jack drill to each programmed position. Logical solution. This is where experience pays dividends. Motion Technologies has a very high knowledge of products including their benefits and limitations. The above was proposed to the customer. What do you think was the outcome? Now the customer did not expect us to turn a solution to the problem so fast, they liked it and asked if we could accommodate for the following. Customer: Can you shorten the drill height from 880mm high to 350mm high? That way we don t have to use a crane and lift the bogie, and we can just roll it under. Secondly, can we drill all 4 holes at once? Motion Technologies accommodated the customer request. Customer invested in non re occurring engineering. 3

4 The base parameters for the project were now changed as below. Automated drilling of all holes at once. Max height 350mm 30 sec drilling cycle Accuracy of holes and hole centers Simple to operate. Operating outdoors. 240 volt 15 amp As the background work had been done on the drills, no change was required to the engineering of this. The concept of how to get the closed height down 350 mm high was the challenge. The result was the bellow drawing Sectional view of the new drilling rig. The simplest way to describe what is happening is to start from center. All components were mounted to a surface ground 25mm thick plate. In the center is a servomotor attached to a gearbox. This gearbox drives two screw jacks. Attached to the screw jacks is a transfer plate that has 4 gearboxes and motors 2 shown above with spindles placed in the 4 gearboxes for the hole saws. The complete fabrication weighed 350kg. The Centre Servomotor and gearbox, along with the 2 screw jacks provide the feed rate for the drills. We chose 2 ton screw jacks for the column strength. This negated the need for additional guidance. The drawing and final proposal was presented to the customer and the he said, Please go ahead, and when can I have it. If you want to know more about Column strength of screws, please read the white paper Critical Factors in Sizing and Designing a Screw jack System by James Porteous For sizing the screw jacks for feedrate of the drills, see white paper from Nicholas Lepper, which provides knowledge on calculating power for a screw jack system. 4

5 Now, Motion Technologies went into finalizing the little things that had to be addressed. Simple things like flooding the drills with coolant in an upside down scenario, which required hollow drill spindles delivering 5 liters per min of cutting fluid. As we had servo motor and drive included in our costing we utilized a specialized drive that has script capabilities for a few reasons, them being we did not need to have a PLC control as the PLC is in the drive which reduces power consumption and one less component. Additionally we could monitor the reflected load from the screw jacks in real time and change federate live based on the wear level of the drilling hole saws. Here is an example of the motion script the servo drive was running. #@AUTOEXEC if (ib[18]==0) home() end if ob[1]=0 while(1) mo=1 if (ib[16]==1) ob[1]=1 while (ib[17]==0) && (ib[19]==1) jv= end while end if jv=0 ob[1]=0 home() end while function home() while (ib[18]==0) mo=1 ob[1]=0 jv= end while jv=0 return #@AUTO_ER #@AUTO_PERR //IS DRILL HOME? //IF DRILL HOME =1, GO TO HOME ROUTINE //DRILL NOW HOME //TURN DRILLS OFF //PROGRAM LOOP //TURN ON SERVO MOTOR //IS GREEN BUTTON PRESSED? //IF GREEN BUTTON PRESSED, TURN ON DRILL MOTORS //IF TOP SWITCH OFF & DRILLS & PUMP ON //THEN MOVE AT SPEED UP "FEEDRATE" //LOOP BACK TO WHILE "3 LINES ABOVE" //IF TOP SWITCH TURNS ON OR DRILLS & OR PUMP OFF //STOP FEEDRATE //TURN DRILLS OFF //GO TO HOME ROUTINE //END LOOP //HOME ROUTINE //IF DRILL NOT HOME "START LOOP" //TURN MOTORS OFF //HOME MOVEMENT SPEED //END LOOP IF HOME, OR GO BACK TO START LOOP ABOVE //FEEDRATE ZERO //RETURN TO WHERE HOME WAS CALLED FROM 5

6 Some pictures of final product: The above movie can be downloaded here Conclusion: Another application Motion Technologies delivered against. Drilling 4 holes upside down through thick steel in a harsh environment. 2 button operation, Automatic drill with Emergency stop. Supplied with load sensing of drills for when drills are worn out. Critical replacement components we designed using local sourced components. I hope you have enjoyed the engineering evolution to the outcome. And to put things in perspective: This mobile drilling rig under trials could drill 4 holes, 24 diameter through 32mm thick steel in 17 seconds. Could a dedicated CNC machine, drill this fast? 6