Resources and calculations for Implement design

[sjk88]

I graduated as a mechanical engineer and am now working as the sole engineer for an agricultural implement manufacturer. Unfortunately this company hasn't had an engineer for some time so alot of the old design and development reports have gone missing. We have recently taken on a project to design a small disc harrow and I am finding it difficult to find any resources on implement design. I have made learnt the basic principles in calculating the specific draft for a tillage tool but I feel that this method is pretty useless when it comes to actually designing an actual implement. Are there any good resources (books, journals websites etc) or a standard set of calculations that can be used in finding necessary design forces such as a practical calculation for draft power and resistive forces on a disc harrow or agricultural machinery in general? Any advice would be a great help.

Thanks

 

[dhengr]

Sjk88:
I am not an Ag. Equip. designer or builder, but I’ve designed and built quite a variety of equip. over the years. I suspect that much of that type info. is pretty closely held, in house, by the various equipment manufacturers. Maybe some Ag. Equip. Manufacturing Associations have some industry design standards, design guides and loading criteria. But, the loads are so variable and the way this equip. is used and misused is so variable, that at best, these would likely be ranges of load possibilities. Obviously, the loads and design are not really life safety issues, as for a building or a bridge, but you don’t want your product falling apart either. The best thing might be to look at your own company’s equip. and that of other manufacturers and sort of reverse engineer their strengths and capacities. You could probably also set up some testing programs to determine a range of loads on a similar piece of equipment and to gather some of the info. you need. What size and complexity of disc/harrow equip. are you talking about? Get out your Engineering Mechanics, Strength of Materials, Machine Design, Structural Design, Welding and Fabricating/manufacturing textbooks and dust them off, you’ll need them. It is more likely than not that you won’t save much money on a new design in cutting out a few pounds of materials, but easy availability of standard materials and components will be important and valuable. Rather..., good clean design and detailing which leads to simple and efficient fabrication and assembly, and maintenance, will pay much greater dividends. You probably aren’t going to reinvent the wheel here, these various pieces of equip. evolved to be what they are over years of improvement and refinement, to do what they are supposed to do, so that should be your starting point. Clean up, improve and refine an existing design. Study and try to understand why things are detailed and arranged the way they are. Your company can hardly expect you to pull this info. out of thin air, after years of running without a real design engineer or a meaningful engineering department. They should have some knowledge of any loads and standards that their equip. should be designed around, that isn’t something that you would bring with you fresh out of engineering school.

GoodLuck!

 

[sjk88]

dhengr:

Thank you so much for your response. I have been digging around the international standards and have manged to find a few ASAE, Phillipino and Indian standards which shed a bit more light on the whole thing. But like you said I think the only way to really figure it out is to reverse engineer some of the older stuff. We do have the advantage of being a fairly well established company, it is just quite sad that this department has been neglected for as long as it has because A LOT of the information that should be here with regards to design reports and the like have dissapeared. To give you and idea of how bad things are I have manged to find 1 design document for the entire range of equipment (past and present) manufactured here, and the calculations used in that document seem very odd, not to mention that the actual implement never went into production. However most of the drawings are still in very good condition and so it is fairly easy to get dimensions and build them up in CAD programs to get an idea of the assembly processes etc.

The implement Im working on is actually a ridger, with 3 sets of small (4 disc) offset harrow gangs running in front of the ridging shoes (so 6 gangs and 3 ridging shoes all hanging off the same toolbar). The problem with the design of this implement is the wieght. The customers request was that we join 2 of our heaviest toolbars together to make a single implement; so in order to satisfy that request in the 1 week i was given to design the whole thing (ridiculous deadline for what we are trying to achieve) I tried to adapt the lightest harrow gangs we have to fit on there. That went a bit wrong but I am trying to redevelop them to make them more rugged without adding too much weight to the toolbar.

Again thanks for your help. As you no doubt have guessed I have plenty of reading to do to.

 

[dhengr]

Sjk88:
Where are you working? You will have to clue me in on some of your parts terminology and their various functions, if you expect me to keep up. Well proportioned sketches and plans, free body diagrams (FBD’s) and calcs., in PDF format, with sizes, dimensions and loads go a long way to defining your actual design problems. You really need to have a good long (or ongoing) talk with your boss. He hired a young fairly inexperience engineer, maybe very capable at the same time, but not a magician or miracle worker either. They let the engineering dept. go to the dogs, and you want to help rebuild it. But, you can’t do this alone or in just one week, when you are also under the gun to get a new design out the door and into production. That’s unreasonable and unfair of him to think or expect. The engineering dept. is a damn important part of the entire process, but not an end in itself either. Can you get in touch with some of the older fellows who called themselves engineers, by whatever training, and made up the old engineering dept? They can be valuable mentors and have experience and knowledge that it will take you time to acquire. There is no doubt that you will CAD and calc. rings around them, that’s what young engineers do to stay on some equal level. But, listen very carefully, read btwn. the lines of what they say and ask lots of question, not dumb questions and not the same question twice, and you will learn a lot that they never did or never could teach you at the Uni. The dumbest question is an important one which was never asked or fully understood. Really try to understand the basics and concepts, do many free hand sketches and FBD’s so you understand the fundamentals, you can always CAD the hell out of things and in fact CAD will draw things that can’t be built practically. Get out in the shop and understand their equipment and how they work, because if you don’t make it work for them, it will never work. The boss should allow you to take these older guys out to lunch, or some such, to enlist their help and mentoring. Bring one of them in for a few hours a week, for a while, if that’s what it takes to get your questions resolved. It is to the benefit of his business to bring you along as quickly as possible, and to provide you with the proper tools and ref. materials, but at the same time not to expect the impossible from you just because you are a graduate engineer. I can appreciate how mind boggling it can be when you are thrown in the deep end of the pool, and told to swim or drown trying. You may have to respectfully adjust the boss’s expectations a bit, as long as you’re a quick learner.

 

[IceStationZebra]

I used to work for the big red company in implements, specifically the test side. I can tell you that most of the basic information you are asking for was learned thru blood, sweat and tears. The actual loads are going to vary wildly depending on the soil type, compaction, moisture, specific ground engaging tools, machine settings and particular farming practices.

Take moldboard plows for example. We knew that the hardest ground to plow in the United States was in western New York and eastern Wisconsin, heavy red clay with lots of rocks. But we had the most trouble with Uzbekistan and Kazakhstan because they had a tremendous amount of hard pan. Customers in Western Europe were very picky about how much plant matter was left exposed. Etc. Etc.

I think dhengr has the right idea. Look at what "the other guys" are doing and the problems experienced with the previous products. Pay attention to general tube sizes and wall thickness. For constant draft load you are limited to ~75% of the tractor mass, but when you turn around on the headlands and drop the implement it will usually see a spike as the tractor is loaded down. Don't forget about roading as you can see some significant accelerations by driving 25mph over rough roads. And lastly if you ship anything by rail watch the loads when they couple the rail cars together (called "humping" loads in the US), they only happen a few times in the life of the machine but they generate VERY high lateral acceleration.

ISZ

 

[sjk88]

Hi

Thanks again for all your replies. When you were doing your testing did you use any reference books, or do you know of any good literature out there just to help get a better understanding of it all. That's the problem with the internet. There is so Much information and all of it is different so choosing a way of doing something becomes more complicated the more you try to read up on these things! At the moment I am using Shingley's Mechanical engineering design and A Textbook of Machine Design by R.S.KHURMI AND J.K.GUPTA for most of the mechanical and structural stuff. Is there anything good out there more closely related to agricultural implement design? Also if you know any good structural design books it would be helpful. I am Using Timoshenko at the moment but I'm not a big fan of the way he's laid it all out. Managed to scavange around a bit and found a page wiith the specific resistance of various soil prep methods in different soils hidden in the office as well which is fairly helpful.

Thanks again for all the help. I really appreciate it!!