
Reduce Time to Launch and Improve Manufacturing Efficiency
Benefits of Using Cannulated Raw Material
Ryan Thornburgh, Business Development Manager, Precision Medical Technologies
Thomas Guéguen, General Manager. Forecreu America, Inc.
Dale Tempco, Orthopedic Industry Consultant
The speed to launch new products in the orthopedic industry has been and continues to be critically important. With increasing time required in early product development and regulatory stages, reducing manufacturing time is one of the few areas of opportunity remaining for reduction of new product launch time. Additionally, contract manufacturers are constantly being pressured to reduce cost. Using cannulated raw material can reduce manufacturing time and improve manufacturing efficiency.
The minimally invasive surgery market, according to Acumen Research and Consulting, is expected to grow at a CAGR of around 9.6% from 2019 to 2026 and reach the market value of around US$ 33.8 billion by 2026.1 Minimally invasive surgery often drives the need for both cannulated surgical instruments and implants assuring the need for such devices in the future.
There are various options available for manufacturing cannulated instruments or implants. Traditional gun drilling machines have been used for years for drilling deep holes. Using cannulated raw material has also been an option that allows many parts to be completed in one machining operation. Drilling within CNC machines has become common using both gun drills as well as specialty deep-hole twist drills. The greatest opportunities for improvement are when parts are currently, or are planned to be, drilled in swiss type CNC machines.
To accurately evaluate using cannulated raw material versus using solid bar one must carefully consider the compete impact of the two options. Traditionally, the comparison of the two options was simply:
Cost of buying cannulated material vs. cost to make the hole in the CNC
Example 1: Cannulated driver, 17-4 stainless steel, 4” length, 0.171” OD, 0.049” ID, AO Quick Connection, T8 Torx
For the example, the cost of 17-4 precipitation hardening stainless steel in .187” diameter solid bar is $1.07 per foot while cannulated material is $32.83 per foot. The cost of the raw material is simply the length of the part times the cost of the material. Allowance for kerf and bar drop need to be considered in determining length. Using part length of 4.0 inches, a kerf of 0.08” and a bar drop of .21” per piece the cost of solid bar is $0.38 and cannulated bar is $11.75. The cost of the raw material can easily be calculated using the following formula:
(Part Length” + Kerf” +Drop Allowance”) x ($ Material)/ft x (1 ft)/12″=Material Cost
To calculate the cost of drilling the cannulated hole in the swiss we must consider both the cost of the time to drill the hole and the cost of the drill bits. To calculate the cost of drilling the hole the following formula is used. A fully burdened shop rate of $70 per hour which includes labor and all fixed and variable overhead will be used in this example along with drilling feed rate of 0.67 inches per minute.
(Shop Rate ($))/hr x (1 hr)/(60 min) x Hole Length” x 1/(Feedrate in/min)=Hole Drilling Cost
Using this formula, the hole drilling cost is $6.97.
Gun drill bits used to make deep holes can be expensive ranging from $90-$140 for small diameters. For this example, we will use $100. Caution must be taken when using these long small diameter drills. A broken drill can result in significant downtime so tool life should be approached conservatively. In this example the drill will be changed after 17 parts. The drill life is then 68 inches (17 parts x 4” per part). The drill cost per part is $5.88 and can be calculated as follows:
Drill Bit Cost ($) x (Length of Hole,inches)/(Drill Life,inches)=Cost of Drill per Part
Comparing the drilling in the swiss to using cannulated material we find that using cannulated material does provide savings.
Drill in Swiss | Cannulated Material | |
Raw Material | $0.38 | $11.75 |
Hole Drilling Cost | $6.97 | – 0 – |
Drill Cost | $5.88 | – 0 – |
Total | $13.24 | $11.75 |
Using the typical simple analysis there is a savings of $1.49 per part using cannulated raw material. At 200 pieces per month the annual savings would be $3,576. The savings are somewhat mediocre. If the part was already in production the cost savings may justify changing to cannulated material. But there is a far greater impact and benefit of using cannulated bar.
This driver, when made from solid bar, has 14.0 minutes in the main spindle and 3.0 minutes in the sub spindle. This would result in a production rate of 4.3 parts per hour as the main spindle operation is the pacing factor. The production rate in pieces per hour is calculated using the greater of the cycle time in the main spindle or sub spindle using the following equation:
(60 min)/hour x (1 part)/(cycle time (min))=Parts per Hour
owever, when using cannulated material, the time in main spindle is 8.0 minutes; cannulated drilling time of 6.0 minutes has been eliminated from the main spindle work. By using cannulated material, the production rate increases to 7.5 parts per hour. This would be an increase in efficiency of 74%! This increase in efficiency can be obtained without additional machine operators or equipment.
Let’s look at another example for a titanium implant.
Example 2: Cannulated Compression Screw, Ti 6Al 4V, 4 mm, 100mm length, 1.4 mm Cannulation, T15 Torx
Solid 0.250″ titanium alloy for this screw is $5.16 per foot while cannulated material is $44.49 per foot. Using the formula above the raw material cost is $1.85 for the solid bar and $15.92 for the cannulated bar.
To determine the cost of drilling a shop rate of $100 per hour will be used along with a drilling feed rate of 0.8 minutes per inch. Using these values and the formula above the cost to drill the hole is $8.33.
Drills will again be changed after making 17 pieces so the cost of drill bits will be $5.88 per piece; the same as in example #1.
Drill in Swiss | Cannulated Material | |
Raw Material | $1.85 | $15.92 |
Hole Drilling Cost | $8.33 | – 0 – |
Drill Cost | $5.88 | – 0 – |
Total | $16.06 | $15.92 |
In this example the savings in using cannulated material versus solid bar is only $0.14. Even at high implant volumes and applying to a family of 4.0 mm diameter screws of various lengths the material savings do not justify using cannulated raw material.
However, when one looks at the increase in production rate, it makes sense to use cannulated material. In this example the main spindle time with solid bar was 12 minutes producing 5.0 parts per hour. With a feed rate of 0.8 inches per minute, the drill time of 5.0 minutes is eliminated from the working being done in the main spindle. Using cannulated raw material results in a production rate of 8.6 parts per hour; a 71% increase in productivity over 5.0 parts per hour using solid bar.
The increase in production rate is related by the ratio of drilling time to the total time in the main spindle. The greater this ratio, the greater the increase in production rates when using cannulated bar.
Ratio=(Drilling Time)/(Total Time in Main)
In the first example the ratio was 6.0/14.0 = .42 which resulted in an increase from 4.3 parts per hour to 7.5 parts per hour – 74%. In the second example the ratio was 5.0/ 12.0 = .41 which resulted in an increase of 71% going from 5.0 to 8.6 parts per hour. In these examples the parts are somewhat long. If the implant in the second example was 45 mm in length, the ratio would be 2.8 / 9.8 = .29. The production rate would increase from 6.5 to 8.8 parts per hour. Even with a short part, using cannulated bar provides a production rate increase of 35%
How would increasing production effect a product launch? We can use implant in the example above. For a launch quantity of 24,000 screws and an average length of 65 mm. The production rate for a 65 mm is estimated at 5.5 parts per hour using solid bar and 8.7 parts per hour with cannulated bar. With 3 machines running 19 shifts per week (3 shifts M-F, 4 weekend shifts) and 7.0 productive hours per shift, it would take 11 weeks using solid bar and 7 weeks using cannulated bar. Using cannulated bar would shorten production by 4 weeks!
For the contract manufacturer, using cannulated bar offers a significant benefit over a competitor using solid bar. Offering a shorter lead-time potentially has opportunity for higher prices. Additionally, using fewer machines can save time and resources needed for capability runs and equipment qualification.
For the OEM, shortening production time can result in additional revenue by launching new products early. This not only increases sales but can offer a competitive advantage.
The most significant impact for manufacturers who are currently gun drilling in their swiss machines is the added capacity that can be achieved using cannulated material. Production rates can easily increase 50-70% when using cannulated bar. Conversion of current production to cannulated stock can add swiss capacity without adding operators or machines. The added capacity can shorten backlogs and offers opportunity to add profitable shorter lead-time orders to fill the increased capacity.
For a contract manufacturer, the gross profit resulting from one shift of parts running on a swiss lathe can be $300 to $600. Machining capacity is usually the limiting factor as subsequent processes are typically batch process such as vibratory finishing, cleaning, passivation, etc. Let’s assume one third of the products being made on swiss machines have gun drilled holes and can be converted to use cannulated material. If the supplier has ten swiss machines and is running 19 shifts per week, there are 9,500 shifts per year. Using a 50% increase production rate using cannulated there would become available an additional 1567 shifts per year (9,500 shifts total x .33 converted to cannulated x .50 increase in production rate). The resulting profits from the added capacity made available by using cannulated bar would be $470,000 to $940,000!
Traditionally, the use of cannulated bar only considered the cost of the raw material. The increase in production rate when using cannulated bar rather than solid bar will shorten production time and can result in significant increase in profits.
References
- “Minimally Invasive Surgery Market Size, Share, Growth Opportunities and Forecast, 2019 – 2026”, Acumen Research and Consulting, 2019.