THE SCREWDRIVER
The Screwdriver is a steel shank inserted into an aluminum cast handle. The part is then face milled and center drilled for the CNC lathe. IT is then knurled in the manual lathe and drop forged in a closed dye to get the rough shape of the flathead. We then grind the head down to shape, harden, and heat treat.
WHAT I LEANRED
While I'd seen some stuff before on milling and lathe work. Forging was a completely foreign process to me, It was defiantly my favorite part of the course, and it showed me how the different manufacturing processes are useful in different ways. Forging gets you a part quick with amazing durability, but often sacrifices some tolerance in the process. It would have taken me weeks to get the screwdriver head to shape with a mill. This project was the one i received the worst grade on, due to my head being out of tolerance. It really hammered home (no pun intended) the importance of measuring twice and cutting once, or more accurately, measuring and grinding in extremely small intervals.
TIPS FOR THE NEXT STUDENTS
Measure frequently and take your time.
Check if the belt on the grinder has been changed, you might be used to it removing material at a slower rate, and zoom right past your tolerance.
COST OF MAUFACTURING BY HAND
Assuming the machines required to make the parts are all accessible, let's look at how much it would cost to make the screwdriver by hand.
(cost rounded to nearest Doller)
(stock priced at McMaster-Carr)
Cast aluminum handle (going by price of 1' x 6' round): $6
steel shank(going by price of 1 ft steel round):$4
cost of labor: 28$
hours spent: 16
total cost: $458
Now thats one expensive screwdriver. If we were able to buy in bulk and automate the process, we would be able to lower the price per unit substantially, Let's think of an automation process, and make 10,000 units
COST OF MAUFACTURING 10,000 WITH AUTOMATION
because we were previously limited to one clock, we had to get the smallest pieces of stock available that could be made into the desired piece. Now we can buy in bulk and cut the pieces to size, which is cheaper. In order to automate the process, there could be a large sum of preset molds for the casting, the screwdriver shanks would be automatically hammered by a programed drop forge and put on a rack where they are then held in the correct place. Aluminum would then be casted into the mold with the shank in place. From here, the shanks could be brought to a large facility with many CNC lathes, which would be programmed to shape and knurl the handle. A closed dye assembly line would then shape the tip, and move the part to a station with girders set at the exact angle desired for the tip shape. The part would be automatically moved to a forge that can heat many screwdriver tips at once, all being held by a rack. the rack would dip into oil, and move to the last step. There would then be another forge for the last heat treat step.
So, what would the cost be?
length of shank: 8.5 inches x 10000 = 85000/12 = 7,083 ft
cost for 6ft of steel: $14
7,083/6 = 1180 rods x 14 = 16,527$
aluminum handle (cast but going by aluminum round size)
4.6' x 10000 = 46000 inches /12 = 3833 ft
12ft of aluminum round stock: $69
3833/12 = 319 rods x 69 = $22,011
total cost= $38,538
cost per unit: $38,538/10000 = 3.85
that's a massive difference! over 100 times cheaper. This goes to show that mass production, and automation is what lets us have complex and well-made things for cheap. Look at any item laying around you. Even if you had all the tools at your disposal, and the knowledge of how to make it, it would take you an unreasonable amount of time to make it by hand.